contact: Jeff Matthews

The Subsoil of Naples — a new translation for this website, Naples: Life, Death & Miracles.

[This is a translation of  Il Sottosuolo di Napoli (The Subsoil of Naples), commissioned and published by the city of Naples in 1967. The entire 500-page work in the original Italian was scanned and made available in .pdf format on the website of Napoli Underground (NUg). A complete English translation by myself and Larry Ray appeared in May 2010 and appeared on that same website. THAT IS NO LONGER THE CASE (!) as that website has gone off-line. I hope to make The Subsoil of Naples available here. It will take some time.

The original Il Sottosuolo di Napoli from 1967 had three parts: the first one is essentially an explanation of why the book was written. That section is directly below on this page (yes, I know it's a screen --humor me) and starts after the next paragraph. It runs about halfway down the page. The second part then starts (on this page). It is all technical geology but a lot of it is accessible even to me (!) and is worthwhile. Of that second part, all 9 sections are now complete (as of 30 October 2019). The first chapter is also on this page. A link is at the bottom to move to the next page). Be patient. The original book had a part 3 to it of graphs and maps, which may not be available.

The Subsoil of Naples is about building and overbuilding in Naples. It was and remains an exhaustive compendium of general geology, the geology of Naples, urbanology and social commentary. Though The Subsoil of Naples is more than 50 years old, it is by no means dated and bears careful reading with respect to the things that have changed and, above all, have not changed since it was written. —Jeff Matthews

[For other material on the topic of Underground Naples, see that portal index.]                         

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This is part 1   Part 2 starts below, here  -   continues here  -         then here  -                         last pages
 (complete)          (complete-part 2, ch.1)          (complete-part 2, ch.2)    (complete-part 2, ch. 3-6)          (7,8,9 all complete)             

1. Introduction (directly below)   2. Table of Contents   3. Formation of Commission, Results & Conclusion

introduction

The Subsoil of Naples

A flood of houses has submerged Naples to an incredible degree. The hills have been assaulted, the greenery destroyed, the entire area victim of building speculators. Whoever now views Naples from the sea stares at a giant cement presepe* clinging to a desolate tuffaceous* cliff.

This is Naples today, the city that nurtured Virgil, the city praised by Goethe. It is a Naples that in the 18th century, driven by the sensational discoveries at Pompeii and Herculaneum, blossomed in its role as capital. Naples then expanded slowly with a few villas along the Chiaia, first towards Posillipo, then still a wooded area, and then with villas towards the green and open plain leading to Portici. Then, in 1812 Murat broke the enchanted silence of Posillipo and her villages and created the now “must see” path, the panoramic road from Villa Donn’Anna to the Cape. The luxuriant woods and vineyards, a sweeter and more human Naples, where an outing into the countryside of San Giacomo dei Capri [an area in the Vomero section of Naples] meant leaving the populated areas of the city behind. All that is still within living memory.
[ed. note: that was written in 1967]

    *[ed. note: presepe - the traditional Neapolitan manger display at Christmas]
    *[ed. note: tuffaceous is the adjective from tuff, a characteristic rock in Naples; it is porous and usually stratified,        
        forned by the consolidation of volcanic ash and dust.]

    This evil manipulation of Naples is recent and a result of the cultural and moral depression in Naples since the end of         WWII. Starting in the 1950s, serious and irreversible changes have been allowed in one of the most scenic areas in the     world; orderly urban development was compromised and the safety and lives of the citizenry blindly put at risk.                 Standing in the way of this havoc have been some urbanologists, intellectuals, and politicians, whose voices have grown     ever louder in an attempt to match the increasing frenzy of the despoilers.

   
    But if reason, a sense of civic duty, and a love of Naples have failed at all levels of responsibility to halt this violent             spread of housing speculation, there is a new, decisive element in the problems of Naples that makes it necessary to         change the way we have done things in the past. As this report make clears, we absolutely cannot delay this; it has to     do with the safety of our people and how what lies below the surface of our city affects their safety.

    We now know, based on this scientific study of great technical importance, that a great overload, both static and             hydraulic, weighs upon the ancient (or inadequate) infrastructure of Naples due to irrational, chaotic urban expansion         over the last twenty years. We now know with certainty that the tipping point, at least in some areas that have been in     balance, is not far off. Earth slides, cave-ins and sink-holes are unfortunately not new here, but their alarming                 frequency over the last few years and the nature of these episodes, especially in the hill areas, comes from a                     progressive deterioration of the supporting subsoil. The underground cavities of all shapes and sizes that have been well     identified in parts of the city aggravate this precarious balance, but they are not, in general, the primary cause.

    This alarming diagnosis has been formulated with scientific rigor by the Commission for the Study of the Subsoil of             Naples; the commission has passed on to the city administration important technical and urbanological                             recommendations. The final report by the Commission will be of great interest to specialists both in Italy and abroad,         but for everyone the report is a valuable lesson and a grave warning.

    It seems obvious that the remedies for the damage caused by past errors, thoughtlessness and abuse, are not to be         found simply in regulations and public works aimed at restoring conditions of safety to the city. Those remedies have to     be undertaken within the vaster context of an urban restructuring of the city, which the center-left city administration         has been cautiously working out. Anyone can see that most of the problems are due to the persistent lack of modern         and functional urban regulation. That regulation goes back to 1939 and will no longer do.

    That basic evaluation sums up precisely the present conditions and the situation we find ourselves in. This investigation     of the subsoil of Naples was promoted and carried out by the center-left administration of the city, and work towards a     new regulatory plan is well underway. All of the material, appropriately coordinated, should be finished in the first             months of the coming year. We emphasize that these plans are a clear about-face with respect to how these problems     have been dealt with in the past. Correct, responsible administrative action will finally assure the city of decent urban,     economic and social development based on a cohesive view of the problems and their solutions.

    It is time to move from planning to getting the job done. Naples has to be restructured for coming generations. We         must give back to Naples her safety, her breath, her greenery and prestige. It will require collective commitment by         cultural and technical forces and the forces of labor, as well as decisive will power of politicians.

    The valiant technicians who gave us this study of the subsoil dedicate it to the coming generation of the 1980s, those         on the frontier of civilization and progress. As head of the commission and as a Neapolitan, I speak for the entire             citizenry when I express my gratitude to them. This work will not be canceled by time or by men but shall remain a         secure guide to the rebuilding the city and shall serve to warn the future as well as accuse the past.

    Naples, October 1967,               [Signed] Bruno Romano

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                                                            The Subsoil of Naples

The digitizing of the original Italian volume was done by Napoli Underground (NUg). Authorization for it was granted to NUg by the Director General of the City of Naples, Doctor Vincenzo Mossetti as directed by the mayor of Naples, the Honorable Rosa Russo Iervolino, and was granted as Project No. 170, dated March 9th, 2010. Special thanks go to City Councilman Salvatore Parisi without whom this project would not have been possible. The original translation was done in March and April, 2010 by Jeff Matthews and Larry Ray.

The term "subsoil" as used here means the various strata of different kinds of soils and rock that cover thousands of square meters of interconnected man-made cavities beneath the city. These cavities include aqueducts, sewer mains, tunnels and the gigantic tuff sandstone quarries that honeycomb areas beneath the city. The Subsoil of Naples is about the problems of building and overbuilding. This report was and remains an exhaustive compendium of general geology, the geology of Naples, urbanology and social commentary. The Subsoil of Naples is more than 50 years old, [ed. note: this was written in 1967] but is by no means outdated. It bears careful reading as to the things that have changed and, above all, have not changed since it was written. Occasional comments have been added as “translator’s notes,” [which are bracketed like this]. The editors appreciate comments and corrections.

The translation notes and introduction are at the top of this page.   

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                                                TABLE OF CONTENTS:

                        Translation Notes & 1967 Introduction by Bruno Romano

                        PART ONE - above
                        Formation of the Commission, report and conclusions

                PART TWO                                                                              
                Chapter 1: Geological considerations - BELOW ON THIS PAGE
                Chapter 2: Geological overview: the city of Naples
                Chapter 3: How mining and underground structures make subsoil shift     
                Chapter 4: The distribution of cavities in the urban area
                Chapter 5: Underground waters
                Chapter 6: A geotechnical description of the urban territory
                Chapter 7: The aqueduct and the subsoil
                Chapter 8: The city sewage system, defects and remedies
                Chapter 9: Causes of movement

Municipal Building Code proposals, test procedures, and other detail-specific data, Commission proposals and soil testing parameters, etc. will be presented in a very abbreviated form following Chapter 9.


                (original p.9) FORMATION OF  COMMISSION, REPORT AND CONCLUSIONS

(A) Formation of Commission. On March 14, 1966, the city council accepted the proposal of public works commissioner, Bruno Romano, to appoint a commission to determine the origins and characteristics of the subsoil of Naples.

                Member of the Commission (also, hereafter in text, "We"):

                President: Hon. Dr. Bruno Romano, Assessor of Public Works

                Dr. Ing. Lelio Saccani, Head Engineer of the City of Napoli
                Dr. Ing. Mario Sgarrella, Head, Dept. of Civil engineering of Napoli
                Dr. Ing. Francesco Saverio Verde, Head, Fire Department of Napoli
                Dr. Ing. Sabattino Meneganti, Dir. Naples District, State Dept of Mining
                Prof. Ing. Arrigo Croce, Full Professor, Technical Univ. Geotechnology
                Prof. Ing. Vincenzo Franciosi, Professor, Construction Science
                Prof. Ing. Pasquale Nicotera, Full professor of Applied Geology
                Dr. Ing. Dante Bardi, Inspector General, State Dept. of Mining
                Prof. Ing. Roberto Di Stefano, University Professor, Expert
                Prof. Pietro Parenzan, President, Southern Italy Speleological Center
                Dr. Ing. Carlo Galateri, Asst. to Technical University Chair, Foundations
                Secretary: Dr. Ing. Guido Vinaccia, Official, Technical Office

Besides these members, we called upon the following experts for occasional opinions and analyses:

Prof. Ing. Luigi Adriani; Prof. Ing. Corrado Beguinot; Prof. Ing. Renato di Martino; Prof. Ing. Paolo Ferrari; Dottor Guido Martene; Prof. Ing. Giuseppe Paolella; Prof. Ing. Giovanni Sapio; Dottor Ing. Silvio Terracciano; Prof. Ing. Carlo Viparelli. These people participated in the final meeting of the commission and assisted in drawing up the concluding report, especially as regards the section on the causes of movement and settling in the subsoil.

B) Commission Goals  
    We were required to turn out a detailed report

        a. with systematic historical data and bibliography;
        b. that included appropriate external agencies as sources;
        c. with accurate topographical surveys of both surface and subsoil;
        d. with appropriate drawings and cartographic materials;
        e. with details of appropriate laboratory work undertaken;
        f. that reflected an orderly and complete geotechnical investigation of the subsoil.

    All of this was in order to determine
        a. the quality and quantity of materials beneath the urban surface, with special reference to the boundaries of                 yellow tuff near the surface;
        b. the movement of underground water;
        c. the location and state of all cavities in the rock and in loose soil above it, with graphics and descriptions;         
        d. relevant geological and archaeological data.

(C) How the work proceeded:

The commission was convened by the mayor, Prof. Giovanni Principe, on 16 April 1966. At the first meeting, we decided to divide the work into two phases; first, a historical and bibliographic study and collecting data and findings from various agencies and societies, including cartographic material; second, coordinating these materials.

(C-1) Collecting data

At the meeting on 13 May 1966, we subdivided the first phase into these parallel sectors:

    a. collecting and classifying geological and geotechnical material about the subsoil (given to Prof. P. Nicotera);
    b. collecting data on existing cavities and on underground hydrology (given to engineer, D. Bardi);
    c. collating and preparing graphics of the above material (given to Prof. R. Di Stefano);

Also, since there had been recent collapses of retaining structures, we turned our attention not only to the subsoil but to surface foundations; this was given to Prof. V. Franciosi, who would draw up plans for constructing retaining walls.

Furthermore, since there had already been a collapse of the containing wall along the street, via Catullo, and since the city public works commission had already appointed a technical staff to investigate the static conditions in the hill sections, this earlier subsoil commission gave us data from their own work by contacting professors Nicotera, Franciosi and Croce on 31 May 1966. As will be seen, these investigations gave us an entire overview of the Posillipo hill. The city public works commission then independently gave us a copy of its findings, with graphics.

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(C-2) Determining the Cavities

For the second phase (C-1b, above) of our work (collecting data on existing cavities), the job of preparing that report was given to Prof. P. Parenzan and S. Meneganti, engineer and chief of the Naples Mining District. Two research squads were formed with Prof. Tempra, vice-president of the Speleological Center, as chief.

The report, “Means and Organization of Surveying the Subsoil of Naples,” was given to us on 31 May 1966 by engineer Menegante. It was the basis for our survey and detailed what had to be done and the time it would take to do it.
(See part 3 for the text of that report)

Then, within our commission, we formed a sub-group to organize the diagnostic phase of the work. Thus, a first temporary nucleus of the Office of Subsoil was set up under the auspices of the Institute of Applied Geology of the Engineering Department of Naples, directed by Prof. P. Nicotera. Above all, we paid attention to preparing cartographic materials of city territory with as much geological data as possible. We note that each member of the commission collected data and made other contributions on his own behalf or that of the agency he represented.

We made requests to the following agencies, who provided materials as indicated:

1. The State Railway: we requested the lay-outs of rail routes and elevation of the underground rail system with relevant documentation from the construction of that system. No data were provided;

2. S.E.P.S.A. [the narrow-gauge Cumana train line]: request made, 26 May 1966 ; eight graphics received, 8 Feb 1967;

3. Central cable-car: request, 26 May 1966; received survey data on the route of that facility;

4. Mergellina cable-car: request,  26 May 1966; no response. Later request, 1 Feb 1967; received 5 fotostatic copes of the tunnel plans of that facility;

5. Secondary Vomero Railways: request, 16 May 1967; received, 28 May 1966, all materials in their possession;

6. Pneumatic postal agency: request on 26 May 1966; answered 7 June 1966. They had no useful data;

7. Naples Gas Company: request on 26 May 1966; they had no useful data since gas lines are on or at the surface but gave us subsoil specifications from the construction of a newer gas line;

8. Superintendent of Monuments: request on 26 May 1966 (for data on ancient cavities of historic interest, catacombs, the Seiano Grotto, etc.). No answer. Follow-up request on 1 Feb 1967; received lay-out and technical subsoil details for the area beneath via Egiziaca a Pizzofalcone;

9. Superintendent of Antiquities: request on 26 May 1966; no relevant data available;

10. A.M.A.N: [ Aqueduct Agency] request, 26 May 1966; reply, 7 June 1966 with available data.

(C-3) Core Sampling

For terrain above the tuff we collected stratigraphic data through 500 core samples from SAF (Fondedile), SAMCEF, engineer Contardi, as well as from the Geotechnical Institute of the Engineering Dept. and from the city of Naples. We studied and evaluated the material carefully and arranged it topographically for later reference.

(C-4) Ordering the material

We kept separate files: i.e. for core samples, underground cavities, bibliography. We evaluated all material for reliability and relevance. Thus, the first documentation of the subsoil was ready and the surveying proceeded.

That complex initial work produced the following grouping of cavities:

    1. those with uncertain location of access;
    2. those with sufficiently approximate location of access;
    3. those already described approximately by existing schematics;
    4. those described in good detail by existing schematics;
    5. street and railway tunnels running straight between two known and well-defined openings.

Further subdivisions might occur within each group as data were refined as to, for example, access locations or reliability of diagrams, etc.

We draw attention at the outset to those cavities in the second group, those with sufficiently approximate location of access. The Subsoil Commission was able to use the services of workers from the City Roads Division, who, on site, gave us precise locations, ease of access, physical condition of the sites and property ownership. A regularly updated “personal registry” of each cavity was kept for the legal and administrative purposes of gaining access to properties.

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(C-5) Survey operations

From the outset we found a net difference (which we had anticipated) between the ancient tufa quarries and those cavities that had been the sites of water storage for the ancient city. In almost all cases, the former are still used and negotiable, while the latter are either clogged with refuse or otherwise completely blocked.

Other noteworthy difficulties had to do with the apathy or suspicions on the part of property owners or tenants, or with unclear relations between landlords and tenants, or by the splintered subdivisions of the property, itself.¹ Those difficulties conditioned or modified our early work in various quarters of the city.

{¹In some cases, areas within the same grotto belonged to, or were rented by, different parties, and subdivided by various walled off areas creating many small sections, each requiring its own separate legal procedures.}

From our work, still going on, a number of cases have emerged of cavities that are totally inaccessible or not negotiable. These sites cannot be dealt with in this first phase of operations due to the high cost of clearing and cleaning them as well as to resistance (both active and passive) from property owners and tenants. In cases where the commission or the city administration cannot resolve this, other solutions, including court orders, will be necessary.

From the beginning, Prof. Patenzan provided the Subsoil Commission with men and material from the Center for Speleology in the South (Naples section), about 20 young speleologists with proper equipment. Alongside of them, from March 1967, there was also a team under the direction of Dr. Armando Falangola; this group went to work immediately under the guidance of the Subsoil Commission.

By 30 September 1967, about 140,000 sq. meters had been surveyed underground; precisely 21,000 sq. meters of underground cavities and 119,000 sq. meters of excavated quarry voids. All of this has meant a great degree of determination in dealing with the problems of deep cavities, particularly given the enormous and complex difficulties in accessing this type of underground structure. This objective (reached in less than a year, if you consider that the first
months were involved with organization and start-up) surpasses the commission’s original, optimistic predictions of 100,000 sq. meters per year.

Our system for representing graphically the cavities seems particularly useful. Besides two-dimensional maps, drawings showed both transverse and, in many case, axial sections with a series of topographical cross sections. A report, often with photos, was drawn up for each survey.

(C-6) Examining the surveys and reported (unconfirmed) locations

We conclude with the topographical surveys. The last phase of work for each cavity was an examination of the underground area, noting the existence of possible static or hydrologic shifting, the state of repair of retaining structures, the presence of otherwise particular geological characteristics (such as, for example, soils weakened physically or chemically, tectonic phenomena, etc.)

We brought cases that were causes for alarm to the attention of the Safety Office of the city administration, whose job, as we know, is to make appropriate repairs. The time limit for our work had been set at 18 months, which was up on 16 October 1967. Even after such a short time and even with the difficulties we encountered (stemming from both the particular nature of the work and, above all, from the skimpy participation of public and private agencies), we feel we can now make the following report to the city administration.

D) Results

We know that a systematic study of subsoil in a case as complex as Naples is not a matter of just a few months; it takes constant determination to research and update. Yet we now feel able to furnish the most ample documentation and most exhaustive statement possible on the subsoil of Naples, given our current state of knowledge.

The bibliography (in part III of this report) lists 478 sources regarding surveys of the subsoil of Naples; they are the principle sources of information in the field. Of special interest are those from the VIII National Geotechnical Congress, held in Cagliari in February 1967, on “The Subsoil of Big Cities.” Based on its investigations, we have been able to identify (as of 30 September 1967) 366 cavities, divided as follows:

—203 cavities (or cavity entryways) at levels beneath their relative entrances at the surface;
—163 cavities (or cavity entryways) on the same level as their relative entrances at the surface;

In the first group we count those voids that have been, or are currently, facilities for some purpose; that is, the Claudio, Bolla, and Carmignano aqueducts; local systems of water storage (the areas in the high city); chambers used in the past for storing supplies; tuff caves beneath factories; and old, abandoned sewers. Entrance to those cavities is by way of well shafts or well shafts and stairs; the stairs were put in during the war so the structures could serve as air-raid shelters.

In the second group are the voids resulting from quarrying stone for construction material (with the voids, often going from the street-level entrances back beneath prominent tufaceous masses for a considerable distance); street tunnels, both ancient and modern; railway tunnels; modern aqueducts; underground Bourbon passageways; and, finally, a good part of the catacombs.

As noted, the Commission identified the best way to survey the cavities within the approximate limits considered in the best technical and practical interests of the city, indicating the presence of such cavities and with the understanding that more detailed studies would follow either by those agencies or those individuals directly interested in individual areas. Our surveys showed this methodology to be the best one.
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Part III of this report lists the cavities and gives an overview plus some examples of the actual files that we prepared. There are also descriptive monographs on cavities that detail the stratigraphy of the 185 core samples.

This material is the first nucleus of what we have gathered about the subsoil; it is material that should then be continuously developed and kept current in the “Special Section for Subsoil” of the Municipal Technical Office, freely available for consultation and serving as an easy and rapid guide for practical use.

Furthermore (see map, below), a geological-technical chart for Naples on a scale of 1:10,000 was prepared; it contains indications for geology, curve of the uppermost level of the yellow tuff strata; location of core samples; and location of cavities. There is also an isopach chart (on a scale of 1:10,000) of the loose terrain covering the yellow tuff.

Chapter 2 of part II of this report describes how those charts were prepared and contains general observations on the eastern and western parts of the city and on the Posillipo hill. All of the cavities with a known configuration have been represented on a scale of 1:10,000 on the tables corresponding to the Topographic Survey Department, STR, of the urban surface. Some of those tables are also included in this report.

The Commission, in keeping with the goals it set for itself at the outset, has also prepared a detailed study of the nature and genesis of the subsoil of Naples; that is found in chapter 1 of part II. We also felt it proper to describe (see chapter 3 of part II) ancient and modern methods of excavating building material in Naples.

On the basis of what we have gathered and presented in this report, we were able to follow the evolution of cavities in relation to urban development over time; that is, we could trace the actual path and chronology of their distribution (see chapter 3 of part II). For material on the course of underground water and variations over time in strata, see chapter 5 of part II.

The geotechnical features of the urban territory is the subject of chapter 6 of part II. We deal with the stratum of subsoil considered technically significant in relation to buildings on the surface and how their foundations are affected. Urban areas are identified that present particular geotechnical problems.

We also deal with both ancient and modern construction and how it has been affected by earth movement resulting from water seeping into the subsoil or by cavities either in the tuff or in the loose soil above the tuff; we look at hillside construction (where the surface is naturally sloped or where it has been terraced for building on properties that are vertically adjacent on the slope), and, finally, with buildings placed on voids built up with artificial landfill.

We have also noted the most recent studies on surveying and building road-beds. We noted with interest the phenomenon of earth movements in the tunnels of Naples, both modern and ancient Roman. These studies gave us indications of how to build such structures in the future. The general situation as to the aqueducts and sewage system was the object of intense scrutiny by the Commission. These two items are dealt with, respectively, in chapters 7 and 8 of part II.

We note the work by an earlier commission on the condition and stability of retaining walls in the hill sections, in particular the Posillipo hill (as covered in the SPEME convention) [SREME refers to the 1926 convention that founded a corporation to build a new quarter of Naples on the Posillipo hill.] Our report and the main graphic material are in part III.

The Commission used studies by Prof. Franciosi, for the design of restraining walls in urban centers (see part III).

The Commission, though not required to do by its founding charter, reserves the right, to express further views in particular cases. We have used chapter 9 of part II to express our views on the main causes of the frequent earth movements that Naples is subject to. We find that our conclusions do not differ substantially from those of the Commission that preceded us [i.e. the S.P.E.M.E study] and hope that they will now attract attention and action.

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Conclusions

On the basis of its work, the Commission herewith presents its conclusions to the city administration:

(1) General recommendations

— 1-1. Urban plans and programs. We recommend that urban plans for restructuring the city (road building both on the surface and underground, new urban settlements, etc.) be verified not just with the usual environmental and geological criteria, but with detailed analyses of factors relevant to the subsoil, especially those contained in this report.

With that recommendation, the Commission stresses the difficulty of such verification and notes that in Naples and elsewhere much construction is not done in accordance with such criteria. Taking these technical factors into consideration can substantially reduce problems in construction and help produce solutions to our urban problems.

     image 1                  

      image 2                            

 

We invite the administration to give this report to the zoning commission quickly so our subsoil can be made safe.

—1-2. With utmost urgency we recommend that the city stop terracing, rock cutting, filling, medium- and large-scale earth moving, and construction of retaining walls unless those works are authorized by the Special Section for Subsoil. We stress that building licenses and authorizations of habitability be granted only after technical reports on the safety of the foundations and sewer systems of the buildings in question. Those licenses shall be granted by taking into account not just the serviceability of private sewage lines and roads, but the certified capacity of public sewage system, public roads, and retaining walls in the areas that handle the additional load.

We thus recommend that the city not permit new housing settlements in the greater urban area unless work on appropriate sewer lines that are to serve those settlements are completed both for new lines as well as upgrading existing ones. We also note that in the new settlement that is to go up in Secondigliano (in accordance with Law 167), that there are no rainwater catchment basins and that work needs to be done to upgrade the facilities that channel off waste water. The Ponticelli settlement likewise needs upgrades to the existing channels.

As to the areas of the high Vomero, Arenella, Pigna, S. Giacomo dei Capri, Camaldoli, and the slope of the Vomero hill descending from the ridge-line of via Cilea-Corso Europa-via Tasso towards the Corso Vittorio Emanuele: that slope is already heavily urbanized, and run-off already flows into insufficient collectors along via Tasso, via Aniello Falcone, and Corso Vittorio Emanuele. The Commission recommends that the city restrict building in that area and not issue further building licenses until these deficiencies are corrected

The Commission recommends once again (see Part III) to the city council that until appropriate maintenance is done on retaining walls, sewer lines and other problems, no further building licenses be issued for the areas covered by the SPEME convention, nor should already authorized terracing, rock cutting, and filling be allowed to go forward.


image 3. The areas marked A through F are referenced in Recommendations 1-3.
       image 3              


Finally we recommend, in any case, that no new buildings overload the existing collectors and sewer lines of the city.


—1-3. The Commission recommends that detailed plans be drawn up for the urban renewal of the following sections of the            city as indicated by letters A-F in image 3, above:

    a. The area of Materdei – Vergini – Sanità, bounded by via Foria (the Botanical Gardens), the Miradois hill (from the         Astronomical Observatory to the Capodimonte Palace), the Capodimonte hill (along the line of the new Tangenziale             highway, the Materdei hill and S. Maria degli Sacalzi to via Foria;

    b. The historic center of the city, bounded by via Foria, via Cesare Rossaroll, Castel Capuano, Rettifilo, via Sanfelice, via     Roma, via Pessina;

    c. The area of Montesanto – Ventaglieri, bounded by via Roma, the rise at via S. Rosa, the slopes of the Vomero hill to     Piazza Leonardo, the military hospital and via Settedolori;

    d. The Spanish Quarters, consisting of the slope (to via Giovanni Nicotera and via Chiaia) rising from via Roma to the         Corso Vittorio Emanuele;

    e. The Pizzofalcone Hill, bounded by via Chiaia, Chiatamone and Santa Lucia;

    f. The area of Chiaia, bounded by via G. Nicotera, via Chiaia, via dei Mille, via Crispi, Corso V.Emanuele, from the             Cumana station the central cable-car station.

The plans to renew these areas should include not just the surface, but the subsoil, as well.

We recommend renewing the surface strata in these areas, including strips along the base of the Vomero and Posillipo hills, and slopes above via Chiaia, Piedigrotta, Mergellina, and Posillipo as far as via Tasso and via Manzoni.

—1-4. As to the efficient maintenance of the sewer system, the Commission recognizes the absolute necessity, in the interest of public health, of immediate intervention by the city administration.

There is much to be done that simply cannot be put off, both in the interest of public health as well as urban stability; nevertheless, in setting up priorities, we stress giving precedence to restoring balance to the city’s water supply.

We recommend that the city, where possible, provide access shafts that permit underground work (particularly on the aqueducts) without interfering with normal services and the damages that might ensue. We call attention to the importance of shielding metal conduits, actively or passively, from stray electrical currents. Public transport agencies should take care not to ground current directly into the subsoil.

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(2) Recommendation for regulations

—2-1. The Commission strongly recommends regulations for the planning, building and testing of:

    a. quarries, both open-air and underground; excavations that expose subsoil or tufaceous material; land-fills                     (incorporating surveys and reports from excavations in major projects);
    b. walls and sustaining structures;
    c. foundations of buildings, particularly those on tufaceous cavities or recent land-fill;

These regulations should, as we detail in Part III, comply with instructions from the Upper Council of the Department of Public Works; regulations shall apply both to private concerns and to public agencies in the city.

We recommend that the administration speedily meet its obligation to have property owners, builders and contractors provide reports on special issues regarding foundations, and, indeed, on any matter relevant to the condition of the subsoil; these reports should be made to the Special Section for Subsoil.

—2-2. The Commission finds the regulations in the Regolamento Comunale (approved in 1942 and still in effect) regarding sewer lines in private buildings to be largely outmoded and no longer valid, especially for these sections: S. Giovanni, Barra, Ponticelli, Poggioreale and the Industrial Zone, which are to be served by an autonomous network with a new water purification facility, now almost complete, located at S. Giovanni a Teduccio.

We thus urge the speedy adoption of a modern, efficient Code that contains, among other things, precise regulations for the planning, building and testing of private and public sewage systems.

(3) Particular Recommendations

—3-1. We know that applyimg these recommendations will take effort from an organizational standpoint as well as a practical one. We thus recommend to the Administration that it hasten to set up an Ufficio Tecnico del Comune (City Technical Office) to handle existing problems and those that crop up in the future. We draw attention to the need for adequate personnel for construction, surveillance, and maintenance of new sewer lines.

—3-2. We hold indispensable a “Special Section for Subsoil.” That section shall work along the following lines:

    a. it shall continue our work and keep collection and updating data on the subsoil;

    b. it shall continue to verify the dynamic condition of roads, both public and private, using existing data as well as             complaints or other reports regarding the stability of sustaining walls;

    c. in building licenses or permits, the “Special Section for Subsoil” shall make its own decision on whether or not the             code for the construction of foundations is being followed;

—3-3. The Commission urgently recommends to the city that it continue with ongoing studies of the stability of the hill areas and provide for the speedy completion of projects, particularly those regarding maintenance of quarry walls and sustaining walls, and with particular emphasis on those sewer lines subject to earth movement since they present a special problem for the stability of the urban infrastructure.

—3-4. The Commission urgently recommends to the Administration that it provide the City with valid, up-to-date maps and charts of the urban territory. The current cartographic documents are insufficient and, in some case, even wrong.

THIS IS THE END OF PART 1 OF The Subsoil of Naples. 

PART 2, Chapter 1 is compete. IMMEDIATELY BELOW.
PART 2, Chapter 2 is complete.

(Oct 16, 2019)

  to portal for underground Naples          to top of this page      

                PART TWO: complete table of contents:
                Chapter 1: Geological considerations  DIRECTLY BELOW
                Chapter 2: Geological overview: the city of Naples
                Chapter 3: How mining and underground structures make subsoil shift     
                Chapter 4: The distribution of cavities in the urban area
                Chapter 5: Underground waters
                Chapter 6: A geotechnical description of the urban territory
                Chapter 7: The aqueduct and the subsoil
                Chapter 8: The city sewer system, defects and remedies
                Chapter 9: Causes of movement

PART TWO: Chapter One

Geological Make-Up

by Engineering Profs. P. Nicotera and P. Lucira

Beyond the Premise and Overview, DIRECTLY BELOW, this long, highly technical "Geological Make-Up"

has these 13 subheadings (in this order, as they appear in the text.) You may link to them individually here:

            THE ANCIENT ERUPTIVE CYCLE IN THE CAMPI FLEGREI          
            RECENT ERUPTIVE CYCLES OF THE CAMPI FLEGREI              
            VOLCANIC ACTIVITY OF SOMMA-VESUVIUS                 
            NATURE AND GENESIS OF THE TERRAIN IN THE SUBSOIL OF NAPLES   
            LAVAS                               
            LAPIDEOUS PYRCOCLASTIC MATERIALS               
            GREY CAMPANIAN TUFF                      
            PIPERNO                               
            STRATIFIED YELLOW TUFF                       
            CHAOTIC YELLOW TUFF                       
            LOOSE PYROCLASTIC MATERIALS                   
            UNDISTURBED MATERIALS                       
            DISTURBED MATERIALS                       

PREMISE

    The urban and outlying areas of Naples are spread in the center of an extremely complex and characteristic volcanic         region that includes the Somma-Vesuvius crater complex in the east to the dozens of craters in the volcanic district of     the Campi Flegrei in the west. Almost all of the urban conglomerate is on land formed by the volcanic activity of the         Campi Flegrei, while the outlying areas, though also connected in large part to the Campi Flegrei, also extend to the         east, to Somma-Vesuvius and have their origins in activity of that volcano.

    In speaking of the subsoil of the city of Naples, whether urban problems or hydraulic and geotechnical problems in a         broader sense, we need to know the geological history of the area. It is only by reconstructing the causes and                 chronology of geological phenomena and petrogenesis that have formed this region that we can understand the                 technical implications in given situations as well as understand the physical, chemical and mechanical properties of the     rock and soil in the region.

    The goal of this chapter is to contribute to a more useful understanding of the technical problems related to the subsoil     of Naples. We have thus tried to outline the geological history of Naples and the surrounding area.

    We first describe the geological history of the Flegrean volcanoes and Somma-Vesuvius; then, we describe the                 characteristics of their geological products and the main phenomena that accompanied the origins of these volcanic         complexes.


OVERVIEW OF THE GEOLOGICAL HISTORY OF THE FLEGREAN-NEAPOLITAN AREA

    The beginning of the volcanic activity that formed the area now occupied by the city of Naples and the surrounding area     goes back to the end of the Pliocene period or the beginning of the Quaternary. Various studies place the beginning of
    Flegrean volcanic activity at the 4th glaciation; that is after the beginning of Ischian volcanic activity but before the         Somma-Vesuvian activity.

    Following the dropping of the “Tirrenide” continental area in the Tyrrhenian Sea, regional fracturing occurred of the kind     known as Tyrrhenian and Appennine. That led to the upwelling of a basaltic magma that, before reaching the surface,         produced various laccoliths, each one of which formed isolated magma basins, themselves. These were, because of         varying local conditions, then subject in turn to their own particular processes of magmatic evolution. These were the         original kernels of the more or less complex volcanic structures that
    then developed.

    Relatively large and shallow magma basins thus formed at Ischia, the Campi Flegrei and Somma-Vesuvius. Each of         these basins developed autonomously, depending on local conditions (tectonics, stratigraphy, depth, etc.).

    The magma basin of the Campi Flegrei, judging from the largely alkalitrachtytic make-up of Flegrean geological                 products, probably derives from a trachyte-basalt magma intrusion noticeably extended vertically, permitting the             build-up of large masses of light magma and differentiated in the higher parts of the basin. On the other hand, the             extreme scarcity of weakly leucitic lava suggests that the roof of the basin is not formed of mesozoic limestone and that     the magma took its position, at a later time, in Tertiary sediments.

    De Lorenzo subdivides past activity of the Phlegrean area into three phases: the first and oldest produced the Breccia         Museo [trans. note: that is the term also used in English. It is defined in various sources as “a pyroclastic deposit             produced during an eruptive event that occurred in the southwestern sector of the Campi Flegrei about 20,000 years         ago.” Apparently, the first use of the term is in Johnston-Lavis. See bibliography] and piperno; the second, yellow tuff;     and the third, pyroclastic products, partially mixed (in part pozzolana) formed by volcanic activity after the formation of     yellow tuff.

                            image 4 

    More recent studies have produced a slightly different picture, including a cycle of activity before the period set by De     Lorenzo, defined as the archiflegrean eruptive cycle, which corresponds to the first and second De Lorenzo periods and     which concludes with the formation of chaotic yellow tuff (known as typical yellow Neapolitan tuff), and, finally, includes     a last cycle known as the recent eruptive cycle of the Campi Flegrei, which corresponds to the third of De Lorenzo’s         ancient subdivisions. Each cycle of activity thus identified is progressively more explosive within each cycle although         that pattern has attenuated over time.
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THE ARCHIFLEGREAN ERUPTIVE CYCLE 

    Activity in the Campi Flegrei started with a long series of eruptions of primarily trachytic nature, the tuff and lava from     which formed a composite volcano (or perhaps a series of such volcanoes) of the kind and size of Somma-Vesuvius.         After a long period of quiet, during which there was constant and progressive build-up of pressure from gasses in the         magma basin, there followed an exceptionally violent eruption that was the origin of grey Campanian tuff, putting an         end to the activity of this Archiflegrean volcano. As a result of the partialemptying of the Archiflegrean magma basin,         there followed a caldera collapse of the central part of the volcano complex.
   
    The boundaries of the large Archiflegrean caldera collapse are not well defined, either because the caldera was                 deformed by other and later local collapses or because the caldera was filled and buried by the activity of at least forty     spin-off volcanoes that later formed over a long period of time within the caldera. In any event, the products of later         volcanic activity deposited on the prominent, preexisting features of the caldera have not erased the traces of the             ancient form; they can still be seen. We can thus see visible traces of the wall in the east that truncated the Monte di         Procida promontory, from Miliscola to Torregaveta, then on the rather steep southern slope of Mt. San Severino to the     north-east of Cuma, then on the northern and eastern edges of the Quarto Plain, on the sunken edges of Pianura and         Soccavo, and, finally, on the northern slope of the Posillipo hill. The form of the eastern region of the Campi Flegrei, to     the east of Camaldoli, is determined by the ancient surfaces of the Archiflegrean complex, largely unaltered even by the     products of later eruptions.


THE ANCIENT ERUPTIVE CYCLE IN THE CAMPI FLEGREI 

    After the Archiflegrean caldera collapse, a number of preexisting, buried tectonic faults were reactivated by the                 rejuvenation of some Tyrrhenian faults, which, besides submerging the northern section of the caldera (the Miseno and     Palumbo shallows), facilitated the rise of magma within the caldera and in the surrounding area, now occupied by the         city of Naples. The peripheral and radial fractures of the Archiflegrean caldera were then superimposed on these             preexisting but rejuvenated tectonic lines, making the entire volcanic-tectonic structure of the Campi Flegrei extremely     complex and often undecipherable.

    Because of the outgassing of magma following the great eruptive explosion of grey Campanian tuff, the Archiflegrean         caldera resumed activity at first with effusive eruptions of smaller volcanoes that led to the formation of flows, lava         domes and scoriae. Most of the volcanic complex of this period was destroyed by later activity or buried by later                 eruptions; the only remaining, visible traces are the ruins of the Miliscola volcano and the alkili-trachytic dome of S.         Martino (both at Monte di Procida).

    With the progressive, thermically retrograde increase of vapor pressure, larger volcanic complexes were gradually             formed, and activity became mixed between effusive and explosive (composite volcanoes) such as the now largely             sunken volcano at Torregaveta of which the only remains are the tuffs and lava flows at the northwest base of Monte di     Proicida.

    From composite volcanoes of mixed activity, there follows, by way of afurther increase in eruptive energy, a series of         eruptions marked by a rapid succession of explosions that emit a large quantity of ash and pumice mixed with little         stones and large blocks spewed upward; Thus, composite yellow tuff volcanoes were born and are different from those     that one still sees at Capo Miseno, Porto Miseono, Bacoli, “Archaverno,” Nisida, Coroglio and Trentaremi. In these             explosive and rhythmic eruptions, the pyroclastic material, still hot and rich with gas that falling near the crateric center     underwent rapid diagenesis, whereas the material falling farther away fell cooler in well-defined layers of ash, pumice         and varying sizes of lapilli or small stones. Thus the same eruption produced simultaneous formation of stratified mixed     rocky tuff and looser pyroclastic materials laterally mixed and gradually turning from one into the other.

    At the end of this eruptive cycle, due to the general build-up of gas in cooling magma, the explosive activity culminated     in a series of extremely violent eruptions that emitted a enormous amount of ash, pumice, and sand in the form of hot,     falling clouds, thus forming chaotic, yellow tuff or typical Neapolitan yellow tuff. Among the chaotic yellow tuff                 complexes that are recognizable today, we note the Chiaia volcano, the Fuorigrotta volcano, and the volcanoes of             Mofete, Girolomini, and Gauro, which is certainly the most recent.

    At the same time as yellow chaotic tuff —or, more precisely— in the interval between two eruptions of yellow tuff, there     was activity at the volcanoes of Soccavo and Pianura (at the base of Camaldoli, on the rim of the Flegrean caldera); the     first of these produced the well-known piperno and the so-called “Breccia Museo,” while the second deposited a whitish     ash-pumice-like semi-coherent tuff. The eruptions at Soccavo and Pianure were followed by earth slides on the walls of     the two emptied volcanic conduits with subsequent chipping of the Flegrean Caldera.

    The eruptions of the chaotic yellow tuff volcanoes should have extinguished after a single violent eruption but frequently     followed by extended collapses; however, these were different in kind from the ones at Soccavo and Pianura because,     rather than simple steepenings of the walls of the volcanic conduits, they were true volcanic-tectonic collapses, that is,     collapses of the dome of the magma basin divided into a number of clumps by radial and peripheral faults such as to         cause regional collapses such as, for example, the collapse in the Gulf of Pozzuoli all the way to the Quarto Plain with         the lowering, as a single block, of the entire volcanic complex at Gauro.

    After the eruptions of chaotic yellow tuff volcanoes, which went on for an extended period (though broken by periods of     stasis, the magma beca me poor in gas and no longer capable of explosive activity. At the end of the ancient                     Campiflegrean eruptive cycle, there were only a few effusions of largely viscous trachytic lavas rising along some of the     collapse faults, which led to the formation of some lava domes such as that of Mt. Olibano.

    Due to the collapses caused by the yellow tuff eruptions, the end of the ancient Campiflegrean eruptive cycle then saw      the sea invade a large part of the central area of the Campi Flegrei, from the Gulf of Pozzuoli to the Quarto Plain, to         Piano, Soccavo and the Fuorigrotta flatland. Out of that sea rose only Monte di Procida and the rest of the volcanic             complexes of Archiaverno, Mofete, Gerolomini, Gauro, Camaldoli and the Posillipo spine joined to the Vomero hill and
    Capodimonte hill to the northeast.


RECENT ERUPTIVE CYCLES OF THE CAMPI FLEGREI

    A long period of inactivity then gradually gave the magma time to build up explosive energy; at that point, volcanic         activity in the Campi Flegrei reawakened with a new cycle of explosive and mixed eruptions.

    One of the first eruptions of that cycle was that at Baiai, followed perhaps at short intervals by those at Minopoli near         Soccavo and, gradually, many others, the chronology of which is difficult to establish, such as the volcanoes on the Baia     sea-bottom, the Gallo-Russo volcano, and then the eruptions, broken by long periods of quiescence, of the volcanoes at     Montagna Spaccata, Pisani andAgnano.

    After the violent Agnano eruption, there must have followed a particularly long period of quiescence, during which time     the volcanic complexes were set upon by the strong forces of erosion (the crater walls had already broken in places due     to the most recent landslides or eruptions). Much material was thus removed or rearranged and the morphology of the     area changed to a considerable degree.

    Eruptions picked up then with renewed violence at Solfatara, followed by the eruptions at Cigliano, Averno, and the         prehistoric eruptions of the Astroni (in the Neolithic, c. 1500 BC), finally ending with the less explosive eruption marked     by strong ejections of scoriae or vesicular basaltic lava at Fossa Lupara and Monte Nuovo (the latter was in 1538 AD).

    Most of the pyroclastic products were not particularly coherent and are partially known as “pozzolano". They blanket         almost the entire Flegrean area with chaotic yellow tuff, are due to the recent Flegrean eruptive cycle.

    The historic eruption of Mt. Nuovo, the bradisismic movements of single huge blocks (for example, in Pozzuoli), and the     hydrothermal and fumarole activity that still persists in Baiai, Pozzuoli, Solfatara and Agnano (that is, along a fault line     in the direction of the Tyrrhenian) attest to volcanic activity still very much alive, if a bit sluggish, and are evidence that     the current basin still contains noteworthy amounts of magma undergoing cooling and solidification.


VOLCANIC ACTIVITY OF SOMMA-VESUVIUS 

    According to Rittman, who reconstructed the history of Somma-Vesuvius in minute detail, endogenous forces had been     keeping volcanic activity in the Campi Flegrei alive for some time when, about 12,000 years ago, the area beneath the     current Somma-Vesuvius was punctured for the first time by a violent explosion, no doubt facilitated by the fracturing     generated by the sinking of the Campanian basin.

    The new volcano that formed is called Somma Primordiale and must have been the site of impressive eruptions as             evidenced by the great amount of ash thrown up in a short period of time. The basin feeding this eruptive center             must have had an origin analogous to that feeding volcanism in the Campi Flegrei and Flegrean islands; that is, an             ascent of differentiated acidic magma through a Tyrrhenian fracture to almost beneath the Mesozoic sediments, thus         creating an independent magma hot-spot over a time that can be subdivided into four periods, which we here briefly         review.

    The products of Somma Primordiale were totally trachytic in nature, as were those of the Flegrean volcanoes. Domes of     very viscous lava formed in the crater of this new volcano only to be fractured and removed by violent explosions that     alternated with effusions until a dome finally formed that was strong enough to resist. That plugged the conduit and         condemned the volcano to a long period of inactivity. Yet, while Somma was pausing, powerful explosions of the                 Flegrean volcanoes were spewing up great amounts of ash and pumice in the form of hot clouds that then settled on         sleeping Somma to solidify as yellow Neapolitan tuff.

    In the meantime, the entire Campanian plain was shifting up and down in a series of movements by separate and             opposing blocks, carryingthe Somma Primordial below sea level along with the yellow tuff that had covered it. Speaking     of blocks moving, it should be noted that because of that, in historic times, the land on the western coast of southern         Italy took on a noticeable inward tilt (i.e. away from the sea); waters flowing on the surface then stagnated near the         coast, producing a number of marshes such as Pianura Pontina, Basso Volturno, and the area of Pesto. The same thing     would have happened at the mouth of the Sarno river if Somma had not reawakened and filled in the land just as it was     tilting away from the sea. This reawakening of Somma took place in around 6,000 BC and was followed by a long series     of cumulative eruptions of the powerful volcanic complex referred to as Somma Antico, the products of which covered     the ruins of Somma Primordiale.

            Images 5-6 (top 2, l & r) - Cavity beneath #59 via Montesanto showing a section of the
            Carmignano aqueduct successively enlarged by the extraction of quarried tuff sandstone.

             Images 7-8 (bottom 2, l & r) Cavity beneath #18 via Broggia, detail of access to the vault.

     [translator's note - the debris piles seen in these photos are typical. Well shafts were used for quick debris removal from WWII       bombings and block many cavities. Unfortunately, shafts and other openings are still used to dump trash and all matter of               waste material into the cavities below the city.]

                                            to top of the this page            to top of Part Two

    Petrographic studies of the Somma Antico lavas (defined as orvietites—i.e. leucititic trachybasalts with leucite) show         that the magma basin continued to rise slowly, reaching the Triassicdolomite that was then absorbed by the magma         with a subsequent change in the progressively deeper and more intense chemical activity of the ejecta from the                 volcano. After another long pause, volcanic activity started again with an emission of “octavianites” (leucititic tefrite         basaltoids) and the formation of the prehistoric volcano we call Somma Recente (or YoungSomma).

    Somma Recente, a typical composite volcano, reached a height of about 2000 meters; after activity in prehistoric             times, it was quiescent phase for many centuries and permitted the growth and development on the  slopes and summit     of luxuriant wooded vegetation until 79 AD when the volcano suddenly came to life again.

    The eruption of that year, which destroyed the flourishing cites of Pompeii, Herculaneum and Stabiae, marked the birth     of Vesuvius and was initially one of “obstructed conduit” (called a Plinian eruption, from the majestic description of the     event given to us in two letters written to Tacitus by Pliny the Younger, who witnessed the eruption.) From that first         eruption down to our own times, Vesuvius has had periods of intense activity alternating with calm intervals, some of
    them centuries long. The products of the volcano are petrographically termed “Vesuvites (that is, leucititic plagioclase)     and constitute a great amount of ash and lapilli as well as copious lava flows that snake down the slopes.

NATURE AND GENESIS OF THE TERRAIN IN THE SUBSOIL OF NAPLES

    After this summary of the chronology of tectonic and volcanic events over geologic time that formed the region                 now occupied by the city of Naples and environs, we move to a short description of the various formations that make up     the subsoil of this region. We examine them from the standpoint of genesis and chemical-mineralogy in order to clarify     their technical characteristics both in sito and as construction material.

    We have noted that the area is made up almost solely of volcanic products of the two eruptive centers, the Campi             Flegrei and Somma-Vesuvius; in fact, even the alluvial deposits and sand are largely modifications of the same ejecta.     In the material that makes up the subsoil of Naples and environs, whether Flegrean or Somma-Vesuvian, whether             deposited directly on the surface or from alluvial or marine sources, we have made petrographic and geotechnical             distinctions in order to provide a classification that better fits the goals outlined at the beginning of this report.

    Thus we have classified the materials under consideration into three large groups: lavas, pyroclastic lapideous material,     and loose pyroclastic materials. In turn, these groups have their own further subdivisions.

    As far as lavas are concerned, we find it useful to distinguish between those of Flegrean origin and those of                     Somma-Vesuvian origin. That distinction fits our purposes, although from a strictly petrographic point of view, it may         seem a bit simplistic.

    For the pyroclastic lapideous material, all exclusively of Flegrean origin, we need to make the following distinctions:         Campanian yellow tuff, piperno, stratified yellow tuff, and chaotic yellow tuff. For loose pyroclastic materials, the               classification becomes somewhat more complex, whether due to the extreme heterogeneous origin of these materials or     to the many factors that may have intervened over time to change the original characteristics.

    To avoid a laborious, complex and not very useful classification, we use a very schematic one. Even if this misses some     of the fine points, it is immediately useful. We see the necessary distinction in loose pyroclastic materials to be                 between disturbed and undisturbed. [Lava remaining where it was first ejected would be undisturbed; that same             material moved or broken up by earthquake or landslide is disturbed.] Disturbed loose pyroclastic materials are further     subdivided, based on genesis and granulometrics, into breccia and scoriae; pumice; lapilli and sand; ash and pozzolano,     other divisions into provenance (Flegrean or Somma-Vesuvian) are also possible. For disturbed loose pyroclastic                 materials, further subdivisionsmust use granulometrics. For these materials, there is no further need to distinguish their     genesis that might significantly influence their geotechnical characteristics.

    This classification (like all, and perhaps more than some) is forced on us by the need for simplicity; we shall see that         there are materials of uncertain origin, for example, between pyroclastic lapideous materials and loose materials, or         between lavas and pyroclastic lapideous materials; there is no way around that inconvenience given the origin and             nature of the materials. We must remember the processes at the origin of these materials and remember our goal,         which is practical and technical.

LAVAS

    As noted, the lavas of Flegrean origin are mostly trachytic, while those of Somma-Vesuvian origin are essentailly             tefritic or plagifloiditic (most of which are ejecta of Vesuvius after the eruption of 79 AD). Vesuvian lava (also referred to     locally as “pietrarsa”) is a characteristic building material in Naples; it is used as street pavement, as cut stone,                 masonry units, fill rubble, and even as breakwater blocks. The main centers of extraction are in Portici, Resina, and         Torre del Greco where lava flows from various epochs are "cultivated” (primarily the flows of 1631 and 1760): the best     blocks are obtained at the center of the flow near the wall called “pietre del pedicino” [an old local reference to the             hardest ‘heart’ or center core of a lava stream], while blocks from the upper part of the “cima” [summit] flow are of         lesser quality due to many vacuoles and general irregularities. The significant physical and mechanical characteristics         are: apparent specific weight= 2.70 – 2.78; wear index (thickness in mm of the abraded surface under a load of 0.1         Kg/cm2 and after a course of 1 Km) = 1.10; breaking load to crushing = 1200 Kg/cm2 (min. 600, max. 1800).

    Rocks of Vesuvian lava are very good for construction blocks, but mot as a base to build on; the lava hides an                 insidious danger in the vast and extended cavities at the base of the flow where the sand-scoriae of the bed of the flow     have been washed away by underground waters. Before building on a lava bed, it is good to check the thickness of the     lava for possible cavities. Trachytic Flegrean lavas are much less widespread; they are found at Mt. Olibano and at             Solfatara, at the base of Mt. Spina, at the Astroni, at the Punta Marmolite of Quarto, at Mt. Cuma and at some stretches     of Monte di Procida. Of these outcroppings, only those at Quarto and Mt. Olibano have been used to harvest                     construction materials: the Quarto trachyphonolites, clearly fluidic, were used by the ancient Romans as road surfacing,     the alkalitrachyte of Mt. Olibano was also used by the Romans in the Pozzuoli amphitheater and also in more recent         times in various Neapolitan monument buildings (Castel Nuovo, S. Francesco di Paola, etc.) and for a number of                 maintenance buildings along the Naples-Roma rapid train line and many highways. The known physical and mechanical     properties of these rock types are: Quarto trachyphonolite, apparent specific weight=2.55; breaking load to crushing =     1200-1900 Kg/cm2; Pozzuoli, apparent specific weight=2.50; resistance to crushing = 400-800 Kg/cm2; trachytic.

    More important than the surface outcroppings of Flegrean trachyticlavas that at these sites are those amassed                 beneath the ejecta of later eruptions and that have often been found in the course of underground work in Naples.             Among these, we note the two trachytic masses found during the building of the Cumana railway tunnel at Montesanto,     the trachyte at Piazza Amedeo at the upper sewage collector and the rainwater run-off collector; the trachyte masses         found in the Posillipo hill at the Naples city sewer effluents of Cuma and Coroglio; and finally the trachytic masses found     in building the urban stretch of the Diretissima [rapid train] tunnel.

    Some reports in technical literature say that all of these lava masses result from effusions before those that produced         yellow Neapolitan tuff. In our view that must be taken with some reservation since there is no longer any doubt that in     the intervals between some eruptions of yellow tuff there were also other particular ones that produced piperno; thus,     the intrusion of trachytic domes could easily have taken place. In any event, whatever the age and position of the             trachytic masses, it is important to keep in mind for very practical reasons that they can be found anywhere in the             urban area, even in those areas that we view as exclusively given over toyellow tuff formations.

LAPIDEOUS PYRCOCLASTIC MATERIALS

    As noted earlier, lapideous pyroclastic materials in the area of Naples (even outside of the city limits) are all of Flegrean     origin. That is not surprising since diagenesis (that is, lapidification) of pyroclastic materials is strictly linked to the             eruptions that produce them. That is, lapidification is not a secondary process that may or may not occur after                 pyroclastic materials are deposited. Lapidifcation doesn’t depend on environmental conditions independently of the             phenomena that produced those deposits in the first place, such as, for example, an elevated degree of amassing from     an overlying load of materials, or the infiltration of water, or the influence of a marine environment. Lapidification is not     due to the particular state of subdivision or the lack of uniformity in the pyroclastic products. Rather, the diagenesis of     Neapolitan pyroclastic materials can be exclusively attributed to the particular conditions present at the moment of the     eruption and precisely to the phenomena of autometamorphism (autopneumatolysis and autohydrothermalization) from     gasses escaping from the mass of deposited and still hot and volatile pyroclastic materials. Only some particular             eruptive activity (described later) has deposited masses of hot pyroclastic materials, rich in gasses, and only in those         cases has lapidification occurred. Somma-Vesuvius has never had eruptions of the type that permit that depositing of         hot, gas-rich, pyroclastic materials. That is why its pyroclastic products have never undergone diagenesis and have         remained loose.

    The degree of diagenesis depends, above all, on the temperature and the contents in the form of gasses of the                 materials at the moment of sedimentation; that explains the shaded, gradual change, both vertically and laterally, of         lapideous pyroclastic materials into other semicoherent and, again, into completely loose pyroclastic materials.

GREY CAMPANIAN TUFF

    According to the most recent views, this tuff is said to be the product of a powerful explosive eruption that put an end     to the original of all Flegrean volcanoes, the great composite volcano called Archiflegreo. In the wake of the powerful         eruption, the central part of Archiflegreo collapsed, producing the Archiflegrean Caldera

    [images 9-13 below] are all of the Cavity beneath #18 via Broggia; a tunnel in inconsistent soils in the zone
                    beneath Piazza Dante showing examples of various solutions for upper cover reinforcement.

                                              to top of the this page            to top of Part Two

    Since this tuff is one of the most ancient products of volcanic activity in the Campi Flegrei, we don't see it cropping up     in its original area where it is buried beneath the products of later eruptions. It is found only at a notable distance from     the Campi Flegrei proper; that is, in the Campanian basin, from Capua to the plains of Angri and Nocera, and on the         Sorrento plain. Normally, the tuff is grey, often shading over to grey-brown, occasionally tending to yellow, and, more     rarely, reddish or violet. The compactness varies; sometimes it can be easily crumbled by hand; other times it is lithoid.     It is characterized by the abundant presence of pumice and small black scoriae in a cineritic mass generally lighter in         color, and the tuff sometimes displays very large scoriae that are foamlike, fragile and irregular. In some zones it has a     flame structure very similar to that of piperno, which has led to it also being called pipernoid grey tuff.

    The eruption of grey Campanian tuff must have taken place in a rhythmic succession of violent explosions sending up         great quantities of mixed ash and lava shreds, with large quantities of gasses, creating a dense and hot suspension          that settled in a chaotic state and then lapidified through autometamorphism. Every so often, the rhythm of the                 explosions must have slowed, allowing for a dispersion of gasses and the cooling of ash and scoriae ejected in those         intervals, which then settled under conditions no longer favorable to complete diagenesis.

    This explains the subtle and gradual changes we see in some zones across the entire series of grey Campanian tuff. In     effect, when you speak of grey Campanian tuff, the boundaries between lapideous materials and semicoherent                 materials or completely loose materials are not precise, so refined is the change from one to the other. In some zones     the lapedeous facies reaches a considerable width (20 to 30 meters and more), while the semicoherent facies is                 reduced to a few meters and less at the wall and roof of the bank. In some zones you have lapideous banks repeatedly     alternating with semicoherent or loose banks only inches thick or, at the most, a few meters, with gradual changes from     one type to another but without appreciable differences that you would notice in the structure of the entire mass or in     the size or frequency of scoriae and pumice.

    That is why we define “grey Campanian tuff” in terms of how it was formed geologically rather than by lithologic type,     thus including in the definition all of the materials emitted during the eruption of this tuff. Then  we specify, if                 necessary, how consistency and cohesive the material is at a given spot. For geotechnical purposes, it is                         important to keep in mind that grey Campanian tuff often has very weak cohesion that, however, still permits the             opening of excavations and almost vertical banks even tens of meters high without the danger of collapse. Likewise,         underground digging is possible without the need for sustaining structures. If, however, you try to extract from one of     the excavations a block that has been cut to a regular shape, that may not be possible because the material will             crumble into an incoherent mass of very fine and ashlike mixture of scoriae and pumice; once the cohesion is                 destroyed, it is impossible to restore or reconstitute the material to its original density.

    That particular behavior of semicoherent grey Campanian tuff is often the source of mistakes by those who lack                 sufficient knowledge of this formation or lack experience working with it. Thus, for example, you might have a core         sample pass through the material and give readings such as “ash with scoriae and pumice” or even “fine sands, slightly     silty with pebbles and coarse sand”. The consequences of such a misinterpretation of a core sample are obvious,             especially if you are laying out the path of a tunnel, for example.

    On the other hand, it is also evident that the weak cohesion of some varieties of grey Campanian tuff cannot always         guarantee stability and safety, especially in certain kinds of leveling work or excavation. To avoid the potential for             disaster, you really do need a case by case analysis by an expert.

    The lapideous variety of grey Campanian tuff is widely used as construction material, especially in many towns north of     Naples, in the area of Caserta, in the areas of Angri and Nocera, and in the area of Sorrento. The physical and                 mechanical characteristics of the material vary from place to place and even within the same general area. On the             average, however, the characteristics vary within the following values: apparent specific weight= 1.20-1.60; imbibition       coefficient in reference to weight= 30-50%; breaking load to crushing= 25-60 Kg/cm2. Some Salernitan grey tuffs have     been found that have a value for breaking load to crushing as high as 150 Kg/cm2.

PIPERNO

    One of the most characteristic volcanic products in Campania is piperno. It has been widely used by Neapolitan                 architects over the centuries and lends air of patrician elegance of many older Neapolitan buildings.

    Piperno has a lapideous look and feel to it. The bulk is typically gray with darker bits scattered throughout, called             “flames”, They are lens-shaped and distributed in roughly parallel fashion. The lapideous consistency of piperno and its     almost fluidic structure have caused various scholars in the past (Von Buch, Zambonini, De Lorenzo) to hold that             piperno was a lava —that is, an effusive rock—  but more recent studies no longer leave any doubt that it is volcanic tuff     — that is, trachytic pyroclastic rock caused by a particular type of eruptive activity known as a “lava lake”. This occurs     when deep magma rises in the volcanic conduit and invades the crater, but doesn’t overflow, thus creating a fluid and         incandescent lake of lava within the crater. From this outgassed, fluid and very hot lava lake, spray and fountains then     shoot up while new, deep and much more viscous magma rises, is pulverized by escaping gasses and ejects in the form     of a fine ash. You thus have, all around the crater, a rain of ash and doughy lava bits that release gasses contained         within them (or from deeper sources) and solidify by pneumatolysis into a single rough mass of lapideous consistency.

    The consensus of opinion is that piperno was the product of a single volcano in the Campi Flegrei, the so-called Soccavo     volcano on the edge of the Archiflegrean Caldera at the foot of the Camaldoli hill. The piperno eruption of Soccavo,             contrary to De Lorenzo’s view, occurred in the interval between two eruptions of chaotic yellow tuff and is thus much         more recent than the eruptions of grey Campanian tuff, which piperno has nothing in common with. The formation of         piperno in Soccavo was accompanied by a coarse and characteristic pyroclastic formation called “breccia museo.” That     formation lies above the piperno bank and was the product of a violent explosion of the Soccavo volcano after the             collapse of part of the volcanic conduit and walls of the crater.

    Other than at the base of Camaldoli, piperno has been found elsewhere in the urban area of Naples, particularly in the     area of Piazza Amedeo/Parco Grifeo, along the extension of via Palizzi and in the Diretissima [train] tunnel (still near         Piazza Amedeo). Stratigraphically, the piperno masses are between two formations of chaotic yellow tuff and, according     to Rittmann, must be from the same eruption that produced the Camaldoli piperno—that is, the Soccavo eruption.

    More recently, however, we have found other pockets of piperno in the urban area, even at some distance from the         eruptive center at Soccavo. We thus  hypothesize that piperno, rather than the product of a single volcano, is more         likely from a particular type of eruptive activity of various volcanoes in the course of eruptions that produced chaotic         yellow tuff. We do not yet have enough evidence to prove that hypothesis, but it is good to keep it in mind for future         studies of the Neapolitan subsoil. Various underground quarries on the Camaldoli slopes with entrances at Soccavo and     Pianura mined this material in the past; these quarries today are almost all abandoned and dangerous. Extraction of         piperno from them is limited to rare cases when the material is for restoration.

    Although this material was widely used in times past in Naples, there are no solid data on its physical and mechanical
    characteristics. Two studies from 1820 and 1869 put values of 592 Kg/cm2 and 151 Kg/ cm2, respectively, for breaking     load to crushing. The first type showed an apparent specific weight of 2.60; the second showed 2.28 (which explains         the low values for resistance to crushing).

STRATIFIED YELLOW TUFF

    This tuff came fron explosive eruptions during the ancient eruptive cycle of the Campei Flegrei before the beginnings of     chaotic yellow tuff eruptions. The distinction between stratified yellow tuff and chaotic yellow tuff is very important             because it lets us define chronological points of reference useful in reconstructing the stratigraphy and tectonics of the     region. The eruptive centers, still recognizable, that produced stratified yellow tuff are the volcanoes at Capo Miseno,         Bacoli, and Porto Miseno, plus the volcanoes at Nisdia, Coroglio, and Trentaremi at the extreme end of the Posillipo hill.      In general, stratified yellow tuff shows a lot of pumice and scoriae, mostly small (although at Nisida there are some         very frothy scoriae that reach one meter in size). Besides the stratification, this formation also shows noticeable                 granulometric differences in the strata and in color and in distinct characteristics that differentiate this tuff from chaotic     yellow tuff (which, as we shall see, even at the roof and wall can sometimes be clearly stratified). Higher up, stratified     yellow tuff gradually shades into a clear grey color, is  semi-coherent and contains numerous bits of pumice and light,         frothy scoriae.

    The eruptions that produced stratified yellow tuff must have been a series of explosions in rapid succession that threw     up large amounts of pumice and ash mixed with scoriae. At the end, the rhythm of the eruptions slowed, extinguishing     in a few last isolated explosions. The rapid depositing of pyroclastic materials, still hot, caused these materials to             lapidify after a final outgassing in situ and to cool slowly. On the other hand, the sedimentary materials that were             thrown up towards the end of the eruption or thrown a greater distance from the crater were already cooled as they fell     and did not undergo diagenesis.

    The same eruption, thus, could have produced stratified yellow tuff and, at a greater distance, an accumulation of             incoherent grey tuff. Furthermore, note that the gradual and subtle change, as one moves upward, from stratified             yellow tuff to semicoherent grey tuff was produced by the same eruptive activity.

    We don’t know the mechanical and physical characteristics of this kind of tuff [trans. note. i.e. stratified yellow tuff].         That is due in part (1) to the fact that it is not widely used as construction material (given the limited extent of                 outcroppings, the difficulty in mining them, and their heterogeneous nature, all factors that discourage practical or             commercial use) and (2) to the fact that this tuff is often commonly confused with common yellow tuff. It is even quite     probable that stratified yellow tuff is more common than we think, especially within the hills that urban Naples rests on;     thus, it is likely that some of the ancient volcanic complexes of Naples are made up of stratified yellow tuff and not         chaotic yellow tuff. That might be of extreme importance from a technical point of view and should be duly kept in mind     as plans are made for new underground lines of communication and new structures that affect the subsoil.

CHAOTIC YELLOW TUFF 
   
    This is also called, simply, “yellow Neapolitan tuff” as if to say that this is the true, typical, Neapolitan rock; it is the         kind most used in construction of all types and the one that lends a particular character to architecture of the region.

    Yellow tuff, which has a chemical composition analogous to that of an alkalitrachyte, is due to the autocementation of         various kinds of volcanic detritus (primarily ash, lapideous lapilli, pumices, scoriae,etc.) that erupted from various active     craters during the ancient eruptive cycle of the Campi Flegrei. The volcanoes known to have produced yellow chaotic...

image 14 - Cavity at via #18, tunnel of the         Carmigmamo aqueduct enlarged for use as         an air raid shelter

image 15 - Cavity beneath                  #59 via Montesanto

image 16 - Cavity beneath       largo Vasto a Chiaia

      ... tuff are Mofete, Girolomini, Mt. Ruscello, Chiaia, Fuorigrotta, and, the last one in time, Gauro. In those areas, where     you can follow the entire series of products, from first to last, of an eruption of yellow tuff, the formation generally             starts (moving up from the bottom) with a series of repeated strata, generally clearly defined and graded, of lapilli,         pumice and ash, mostly well diagenetized —that is, yellow stratified tuff. Among the cineritic strata there are some that     contain numerous and typical pisoliths. As you move up, the stratification gradually disappears and then changes             abruptly to a typical chaotic yellow tuff mixture of fine ash and coarse sands, voluminous and relatively light pumice,         heavy re-disgorged blocks, and scoriae and lapilli. The mixture is unstratified and random-like throughout the mass.         Further up, the yellow chaotic tuff, in turn, changes gradually to stratified tuff that terminates in a much less coherent,     clear-grey cineritic facies popularly called “mappamonte.”


    The mechanism of an eruption of chaotic yellow tuff was described in detail by Rittmann, who studied the succession of     materials in a number of complete samples of yellow tuff. He provided us with a very effective description of this kind of     eruption. We provide that description here, below.

    The structure and texture of yellow tuff make it resemble some ignimbtites, some deposits from hot clouds, and lahars;     that is, it is mixed pyroclastic material thrown in such quantity and in such a short time as to form an extremely hot         and very mobile suspension that inundated vast areas at great speed. That is the only mechanism that explains the         perfectly chaotic nature of the tuff, the partial devetrification of its pumices, and its exceptional firmness. The                 devetrification of the pumices is evidence of slow cooling and shows that the material was still very hot when it was         deposited. One also finds, here and there, tiny crystals of pneumatolytic minerals, which shows the presence of                 extremely hot gasses that produce not only neoformations of pneumatolytic minerals, but also recrystalizationsand         devetrifications that strengthen the mass.

    The mechanism of an eruption of yellow tuff, according to Rittman, is the following:

    An enormous amount of magma, very rich in gasses but not very hot and, thus, viscous, rises in the conduit, pushing         ahead of it a mass of cooler and more viscous lava. Once at the mouth, this mass forms a dome that spreads out             laterally, clearing the way for more magma from below. That magma then explodes in a rhythmic series, throwing up         stratified material. The rhythm accelerates and culminates in a gigantic explosion that emits such a quantity of                 pyroclastic materials of all dimensions that, with the gasses, it forms a dense, heavy suspension that is unable to rise         very far. It settles quickly in the form of hot clouds that overflow the crater and move down the slopes at great speed.     The speed of these settled hot clouds is remarkable and lets pyroclastic materials suspended in the hot gasses move         tens of kilometers, depositing great amounts of chaotic tuffalong the way. The make-up of the main mass is chaotic,         but the upper parts of the hot clouds are less heavy and coarse; thus, a small amount of ash remains suspended a bit     longer and deposits itself on the roof of the chaotic tuff, forming the “mappamonte.”

    The hypothesis formulated by Rittmann on the genesis of Neapolitanyellow tuff has been completely confirmed in work     done by R. Sersale, who reconstructed the genesis of volcanic lithoid tuffs by a process of zeolitization and ensuing         hydrothermal treatment of incoherent pyroclastic material (pozzolano) under precisely controlled environmental                 conditions.

    The volcanoes that produced yellow tuff must have all erupted on the surface because a tuff that is so chaotic cannot         form under water, where there would have been, in any case, a rigorous sampling and because the slopes of the craters     are too steep to have formed underwater; also, the stratified tuff immediately below the chaotic tuff displays many         characteristic pisoliths that are, beyond any doubt, the products of a surface eruption and not an underwater one. The
    presence of some single shells means that the volcano that produced this tuff may have formed near a beach, in             shallow water, incorporating some shells, but the crater, itself, rose on the surfaceand, not underwater.

    Between eruptions of settling hot clouds and explosive rhythmic eruptions, there are mixed, intermediate types that         produce more or less cineritic and stratified yellow tuffs. Similar tuffs can also form around the edges of hot clouds. This     would explain the variation in facies that we se in different areas, especially at the edges of the north-eastern urban         area, where we find a gradual lateral shift from chaotic yellow tuff to loose, more or less stratified pyroclastic products.

    As Rittmann rightly notes...

    ...the formation of chaotic yellow tuff is bound to a certain eruptive mechanism and, thus, to a certain evolution of             magma that determines its viscosity and content of gasses. We can add that this is a very advanced state in the             evolution of magma, but that is not to say that all the magma in the Flegrean basin reached that state at the same         time. Rather, it seems that the necessary conditions came about at different times, in single conduits or single small         branches such that yellow tuff is not strictly characteristic of any given period in the Campi Flegrei. Geological surveys     in the area have, in fact, shown that yellow chaotic tuff formed at various times both before and after the Soccavo             eruption that produced cineritic and pumice tuffs, piperno and brecce. The stratigraphy of the Campi Flegrei thus seems     more complicated than the subdivision into three periods proposed by De Lorenzo. In reality, there are different                 “periods” of yellow tuff. Given the lithologic similarity among the different tuffs, however, it is not easy to establish the     order in which they appeared unless we can determine their positions in the strata in which they are interspersed with     more characteristic tuffs.Unfortunately, the outcroppings are scarce and isolated, such that we can’t trace single strata     for any great distance along the surface.


    Very accurate petrographic, stratigraphic and tectonic studies based on grading and leveling, drilling, wells, tunnels, etc.     might solve some of these outstanding questions, questions that are interesting both scientifically and from a practical     point of view. It is evident that reconstruction of the stratigraphy and tectonics of the urban area and the areas of             future expansion of the city would be very helpful in solving the technical problems relating to the subsoil of the city.

    We have already said that yellow tuff is the most widespread and plentiful construction material used in Naples. Its         physical and mechanical properties, however, are quite variable not just from place to place, but even within the same     quarry. It is not at all rare to have tuff classed and priced according to variety right in the quarry, itself. Quarry workers     use different terms for these varieties: thus, we have “cima di monte” [top of the mountain], “pietra arenosa” [sandy         stone], “pietra dura” [hard stone], “pietra ferrigna” [ferrous stone] and “pietra fine” [fine stone].

    The most sought-after variety is “fine stone,” not because it has better physical or mechanical characteristics than the     others, but because it has a more uniform, fine and compact grain, making it easier to handle with a mason’s special         “hammer.” Dell’Erba, in a classic treatise on the subject, described with abundant data from hundreds of samples the         various kinds of yellow chaotic tuff. The variety that showed the greatest degree of mechanical resistance was the             so-called “ferrous tuff” found towards the roof of the formation in the transition zone to “mappamonte.” According to
    Dell’Erba, this variety has an average resistance to crushing of 126 Kg/ cm2. There are, however, even more resistant     tuffs (as high as 175 Kg/ cm2). Besides the resistance to crushing, there are also, within certain limits, variations in the     physical characteristics: the apparent specific weight varies from 120 to 170; degree of compactness from 0.50 to 0.70;     the imbibition coefficient in relation to weight, from 0.20 to 0.40. In general, however, the average values for the most     common kind of yellow Neapolitan tuff are the following: apparent specific weight =1.23; imbibition coefficient in             relation to weight = 0.37; resistance to crushing = 50 Kg/cm2.

    During the digging of wells, shafts and tunnels in common yellow chaotic tuff, there were areas of various size and form     made up of a compact green-grayish tuff.  M. Guadagno first noted this in 1924 in the Santo Stefano area of Vomero.         Then, in 1925 in the Luigia Sanfelice area of Vomero, they found other masses of green tuff in yellow tuff. This was         noted by Salavtore, Friedlander and in a petrographic study by Rittmann. More recently, in1949, during work on a well     shaft and tunnel of the Naples aqueduct in the Vallone Ricciardi and Santo Stefano areas of Vomero, Nicotera did an         accurate petrographic study on a variety of green tuff as well as on the yellow tuff surrounding it. He found that the         “inclusions” of green tuff were of various form and size, but thst they provided no clue in reconstructing the original         process of stratification. That is, the transition from green to yellow tuff was abrupt and clean, but that is seen only in     the yellow varieties of tuff either in the grain or in the change, itself. The rest —the structure, grain, and size and               distribution of the embedded pumice and rock— showed no difference.

    The petrographic study showed, beyond any doubt, that there was no noticeable difference in the composition of the         quantity, nature and size of the pumice lapilli or other lapideous bits in the basic cineritic mass (the yellow variety was      yellow-ochre; the other variety was grey-greenish).

image 17

image 18

image 19

Front view of excavation, foundation work for building construction in incoherent volcanic soils (along via Nuova Camaldoli, images 17and 19) and in soils in this report (fig. 18 in the San Giacomo dei Capri zone.)

There was only a slight difference —a higher degree of freshness [retention of color] in the pumice embedded in the green variety. After a few hours of treatment in a solution of hydrogen peroxide, green tuff became indistinguishable from yellow tuff. Later tests on greenish tuff showed that the difference between these two varieties is a matter of degree of oxidation. That explains why we never see outcroppings of green tuff except at freshly dug sites. Guadagno thinks that the masses of green tuff are the relics of an original green tuff, almost totally oxidized and transformed into yellow tuff. Salvatore says, however, that the greenish areas might be the product of “intimate, secondary reactions” that happened in the tuff after it was formed. In any event, we can exclude that the type of greenish tuff found as “inclusions” in yellow tuff is the same as the grey-green tuff found in various deep wells at the base of yellow tuff (such as those described by F. Ippolito in the port zone of Naples, or by Guadagno at the well in the square of Santa Maria la Fede or, yet again, by D’Erasmo in some of his works). That tuff is to be attributed to the formation of grey Campanian tuff, the product of volcanic activity that occurred before the activity of yellow tuff. We can’t even group this type of green tuff in with the green tuff of Epomeo in Ischia, which we often find in redisgorged blocks in with the yellow tuff of Campi Flegrei. As a matter of fact, the tuff from Epomeo has a stable green color, not oxidizable, given it by the presence of minute tags of a mineral in the glauconite group.

During the construction of the Vomero tunnel of the Circumflegrean railway, a large (longer than one meter) fragment of fossilized wood was found in this kind of oxidizable greenish tuff. The fragment was 250 meters to the east of Torre San Domenico; it was at a depth of 20 meters and 80 meters above sea-level. Carbon dating put the age of the fragment at about 10,000 years. This dating shows the antiquity of the Flegrean eruptive phase that produced yellow Neapolitan tuff; it fits perfectly with the chronology of Flegrean-Somma-Vesuvian volcanism reconstructed by Rittman. Even from a petrographic point of view, there were practically no differences between the kind of greenish tuff found in the areas of S. Stefano and Vallone Riccardi in the Vomero hill, and the corresponding kind of yellow tuff and the physical and mechanical characteristics of the greenish tuff were notably better. The green tuff from Vallone Riccardo showed a resistance to crushing that varied from 116 to 166 Kg/cm253 while green tuff from S. Stefano actually reached 230 Kg/cm2, the highest reading ever recorded for all types of Neapolitan volcanic tuff. It should be noted that the surrounding yellow tuff also showed elevated readings, but noticeably lower than the green tuff embedded in it.

We have spent some time discussing this greenish tuff (which is practically the same as yellow chaotic tuff) because it forces us to dwell on the proper interpretation of stratigraphic samples done in the past in urban Naples. Such samples showed the presence of grey-greenish tuff at a depth where we might have logically expected yellow tuff; in effect, we can’t exclude the possibility, in some cases, that it is all the same yellow tuff formation.

This underscores, all the more, the need to study wells, excavations and core-samples with caution in order to avoid false interpretations that can lead to noteworthy consequences both from a scientific point of view and a practical one. Yellow tuff is present in banks that range widely from zone to zone in the city: up to more than 180 meters in the area of ex-Piazza Leopardi in Fuorigrotta; up to about 110 meters in some areas of the Vomero hill; around 60 meters at and around Piazza Vittoria; around 90 meters in the area of Piazza Plebiscito; around 50 meters in the area of Santa Marria della fede; and 30-35 meters in the eastern part of the urban conglomerate. These data are sporadic and scattered because there are really only a few stratigraphic core samples across the entire range of the formations of chaotic yellow tuff. It is certain, however, that the yellow tuff in the urban area is not formed as a single bank but, rather, of superimposed, mostly horizontal layers or strata of lapideous chaotic tuff (each one of which representing a single eruption), separated by levels of more or less coherent pyroclastic materials (representing the beginning or the end of an eruption of yellow tuff) interlaid with banks of piperno, accumulations of volcanic brecce, and expansions of lava. Furthermore, it is certain that towards the eastern edge of the urban conglomerate the yellow tuff formation thins out until it disappears altogether. In its place we then find loose pyroclastic materials, either Flegrean or Somma-Vesuvian, as well as alluvial deposits transported from various sources.

The yellow tuff formation must have undergone many powerful tectonic dislocations, (primarily a lowering) caused by a series of collapses of the roof of the volcanic basin following the emptying of the basin of enormous amounts of magma in the form of hot clouds. That is why yellow tuff then split into various clumps affected by frequent fracturing grouped along tectonic lines of movement below. Furthermore, in the mass of yellow tuff there are many other regularly occurring and characteristic fractures and lithoclasts due to the contraction of the diagenetized (by autometamorphism) cinaretic mass after cooling. Finally, before being mantled and partially buried by later eruptions (by mostly loose cinerites and pozzolana) the yellow tuff formation was exposed for a long period of time to violent erosive atmospheric activity. (This occurred in the relatively peaceful period between the ancient and recent eruptive cycles of the Campi Flegrei.)

All this produced an extremely complex morphology buried in yellow tuff, one that is often different from the one we see today. In this mass of tuff —dislocated, faulted, fractured and eroded— abundant other loose pyroclastic materials have superimposed themselves, partially filling in the furrows, leveling and softening the once jagged and irregular morphology. Added to the leveling effect of the recent Campi Flegrean eruptive cycle, we now have to deal with manmade effects, which have often filled in valleys and leveled bumps and irregularities. This has made it all the more difficult to reconstruct the original course and pace of the tufaceous subsoil. That can only be done by patiently selecting, collecting and studying all of the current and future data that pertain to the urban subsoil. That work has already started and is the subject of the next chapter in this report. The work is just beginning and is a long way from reaching conclusions.

For many centuries, people preferred to mine chaotic yellow tuff for construction not from embankments or open-air quarries but from underground sites. This was probably because they wanted to build the structure from material mined right on the spot rather than transport it from farther away. There were two different methods for extracting the stone: one was to dig a vertical well through the loose pyroclastic material above the stone. Once into the stone, they gradually started to expand the cavity out into a bell-like shape. A second way (possible only under some conditions) was to dig a horizontal or slightly downward angled shaft into the tuff, then cut out large chambers off the shaft, and extract the stone by way a series of deepening excavated layers, or rarely, a series of excavations which lowered the overhead ceiling in a series of steps as the tuff strata encountered loose pockets of subsoil. This topic is amply covered in another chapter of this report by R. Di Stefano, who has reconstructed the distribution, development and evolution of underground excavations in the Neapolitan subsoil over the centuries.

At this point, we simply note their presence of these cavities and the presence of any number of other items such as cisterns to hold rainwater and, then, water run in from the aqueduct. These excavations and cavities can, in some cases, have a direct or indirect influence on the stability of the buildings above them. They can also (1) put serious obstacles in the path of important underground work on the urban infrastructure (such as, for example, building an underground train line) and (2) also sometimes be used to the advantage of such public works. We have direct knowledge of many cases. As far as the first one goes, we cite the case of the first station of the Flegrean railway line at Montesanto; completion of the station was held up for years by the difficulties encountered in trying to expand one of the two existing tunnels; the tunnels are hard up against, or even partially run through, a deep and vast cavity that is in ruins and supported by a series of monumental buttresses, arches and columns. As an example of the second type of situation, we cite the case of the main SIP telephone center on the hill at Mt. Echia, where a number of vast cavities were found, some of which went down to the level of the Galleria [tunnel] Vittoria of Chaitamone, that is, about 40 meters deep. These cavities were used to create a large underground storage facility. These two examples, on either extreme, show the great importance of knowing about the Neapolitan subsoil in any plan of urban expansion; they demonstrate the need for organized investigations in order to map our subsoil, a great part of which remains unknown even today.

In this chapter we shall not deal with the effect that this extensive underground network of cavities might have on the stability of structures both on the surface as well as underground. That is handled in the chapter dedicated to such problems as cave-ins, collapses, etc. brief mention of some of the chemical properties of the rock, information that has only come to light in recent years. Detailed studies by R. Serslae have shown that...Yellow Neapolitan
tuff, contrary to what we used to think until just a few years ago, is “hydraulically reactive” (that is, it reacts with calcium hydroxide in water to form products with cement-like properties) even more so than pozzolana, the material used to make hydraulic mortar. It is evident...(cont.)

image 20

image 21

image 22

Back filling of Sgambatati  at San Giacomo dei Capri, to provide a new soil base for construction; front view of the progress of removal of soil in the report (image 20), excavation for creating supporting foundation for piling (image 21), examples of strata of incohesive volcanic materials (image.22).

(cont.) that, at least in the area of Naples, this new information is largely of scientific interest; that is, as long as we still have high quality pozzolana, there is no advantage to using yellow tuff, which would first have to be finely ground.

To complete the examination of Neapolitan yellow tuff, we now make Finally, some current investigations at the laboratory of Health Engineering of C.N.E.N. (Comitato Nazionale per l’Energia Nucleare) [National Committee for Nuclear Energy] have found that yellow Neapolitan tuff has excellent exchange properties as regards two longlived radionuclides, Cs 137 and St 90; the yellow tuff has exchangeproperties clearly superior to those of other natural exchangers (montmorillonite and vermiculite), such as to render yellow tuff competitive with the best inorganic exchangers for the treatment ofwater contaminated by refuse.

LOOSE PYROCLASTIC MATERIALS 

As noted earlier, loose pyroclastic materials are quite difficult to classify. This is due to the great variability in types as well as to the different conditions of genesis and the many external factors that later intervened to modify their original characteristics. For those reasons, we have chosen to distinguish between undisturbed and disturbed material. [trans. note: “disturbed” in this context means moved from its original position.] In our view, the action of disturbing [or moving] the materials either by external dynamic events or by man, is almost always what causes their mechanical and physical characteristics to change. With that, we now rapidly review these materials, limiting
ourselves to their genesis and petrography and at how those factors anfthe structure of the materials influence the physical and mechanical characteristics.

UNDISTURBED MATERIALS 

The materials have been divided, in part, along the lines of their genesis and, in part, their granulometrics. The basic types are: volcanic breccia; scoria; pumices; lapilli; ash and pozzolana.

volcanic breccia — are made up of a coarse accumulation of lava fragments (and other rock) produced by the explosion of an obstructed conduit or torn by the explosion from the walls of the conduit; they may also be material that has collapsed from the sides of the mouth of the crater into the conduit and then been ejected. In general, breccia are a mixture of fine materials and represent sporadic episodes of volcanic activity. The classic case is that of the “breccia museo” (so-called because of the great variety of rocky material it contains) on top of the piperno and in part of the Soccavo piperno eruption at the base of the Camaldoli hill. In volcanic breccia we sometimes see the phenomenon of pneumatolysis, a determining factor in certain kinds of diagenesis, but, generally, the breccia are present in a loose, incoherent state. We find masses of volcanic breccia in some underground cavities in the urban area (for example, in some tunnels of the new aqueduct). Pinning down their exact location would be be very useful in reconstructing the stratigraphy of the subsoil of Naples.

scoria — can be divided, depending on their genesis, into “ejected scoria” and “lava socriae”. Ejected scoria are lava shreds thrown from the mouth of the volcano during the eruptive phase, in fact, now named for that activity of scoria ejection. These breccia are only moderately frothy, but in their entire mass are made up of a glasslike substance containing sporadic intratelluric crystallization. Sometimes the shreds settle when they are still liquid or doughy and are thus flattened at contact with ground, often fusing themselves to one another, producing a so-called “fused[or welded] scoria formation.” Piperno is a special case of welded scoria. Lava scoria, on the other hand, are made up of a substantially compact lava nodule the outside of which has a foamy or frothy crust, rough and irregular, on which you find flakes of pneumatolitic minerals.

Lava scoria form the upper and lower parts of a lava flow where the material takes on a frothy look due to the escape of gasses and then a glassy appearance because of the rapid cooling. Among the most common and important lava scoria is the so-called “ferrugine” [ferrous, metallic] variety, which is of Vesuvian origin. It is widely used in Naples for the production of light, cement-like mixtures that are highly resistant. Ferrugine owes its properties as a construction material to its make-up and structure, combining the mechanical resistance of lava with high adhesion and low weight.

From the foregoing, it is clear that there is a substantial difference between lava scoria (i.e. essentially ferrugine) and ejected scoria. In the latter, we have lava shreds dragged into the air by erupting gasses and cooled in flight into a black mass of frothy glass (with an occasional lava nucleus). Lava scoria, on the other hand, is substantially microcrystalline with little glass on the surface. Ejected scoria are more frequently the product of Flegrean rather, than Somma-Vesuvian volcanism, while Flegrean lava scoria practically don’t exist at all. That is not chance; it is a direct result of the chemical composition of the two magma types. The size of the scoria, whether ejected or lava, vary a great deal, from a few cubic decimeters [trans. note: for example, 4 cubic decimeters = 244 cubic inches] and larger all the way down to sand.

pumices — are shreds of lava of various sizes, from the size of a pea to that of a human head. They are very frothy and glass-like, extremely porous and light, and are ejected from explosive volcanic activity, almost always during the initial phases. Alomng with pumices, even larger amounts of ash are thrown up, but during their flight through the air, they are sorted on the basis of their weight (and, thus, size) and settle in strata that are granulometrically quite distinct. If, however, the pace of explosions accelerates, that sorting process no longer occurs and the pumices then settle together with ash from earlier explosions, producing a mixed mass of pumices and ash.

Pumices are generally formed from very viscous magmas. The very porous rhyolitic pumices (for example, those found on the island of Lipari) are typical and plentiful; trachytic pumices (such as in the Campi Flegeri) are less finely porous, but still relatively plentiful. Pumices are less frequent in Vesuvian magmas unless, after a long period of blockage in the conduit, there conditions that allow them to form (i.e., a chemical-gravitative differentiation in the magma and a build-up of gasses in the upper part of the conduit), which is what happened in 79 AD in the initial eruption of Vesuvius, which destroyed Pompeii under a blanket of pumice and ash. On that occasion, the bank of pumice reached a width of 2.5 meters at some points, but that is a unique case in the 2,000 year-old history of Vesuvius. [trans. note on “initial eruption”: By definition, “Vesuvius” starts with that eruption. Obviously, the earlier volcano named Somma has a longer history of activity.] Since that eruption, pumices have been a negligible part of the products of the volcano. Pumices are widely used in cement-mortar mixtures to make blocks, hollow bricks, etc., which due to  the low weight per volume, high moisture resistance, and fair mechanical characteristics lend themselves very well to the construction of non-load-bearing structures.

Among the pumice banks from the recent Flegrean eruption and well known to old-time Neapolitan miners is the one called “sette palmi” [trans. note: seven palms, one palm being a unit of measure based on the hand-span] because it was about two meters thick. Until a few years ago (and possibly still today) pumices were extracted from a series of unreinforced underground shafts dug down and then branching off into the subsoil of Naples. This practice is now forbidden because it led to potentially dangerous conditions and was the cause of at least some cave-ins.

In that respect, we might cite, among other examples, the case of the recent, huge cave-in on via E. Cortese in the Vomero section of town; that cave-in brought to light an old shaft dug in a pumice bank just a short distance from sewer lines. The shaft evidently promoted further erosion from a leak that had originated at the sewage line; once that erosion started and expanded, it produced a vast underground cavity, tens of meters deep and causing the collapse of a large stretch of road-bed (fortunately with no victims).

lapilli — The term lapillo (the singular) [little stone] has a strictly granulometric meaning; it indicates loose pyroclastic materials roughly the size of fine gravel or pebbles. We thus have to define the genesis and nature of lapilli (lapideous, scoria or pumice) in order to define their physical and mechanical characteristics. In the terrain we studied, lapilli, (except in the case of pumices) are found in banks a few decimeters in width at the most, and they alternate with other loose pyroclastic materials. If we finder thicker banks of lava lapilli or scoria that are granulometrically uniform, they are certainly disturbed materials from an alluvial or marine environment. Naturally, lapilli may also be found frequently in mixed accumulations of loose pyroclastic materials and all other products of explosive activity.

ash and pozzolana  — Volcanic ash is a collection of extremely tiny shreds of glassy and frothy lava. It has a small bubbly texture and is mixed with other vitreous and non vitreous detritus, among which are fragments of intratelluric crystals and rock ripped from the walls of the conduit by erupting magma and gasses. In the area of Naples, volcanic
ash is more or less rich in pumices, lapideous lapilli and scoria from both Campi Flegrei and Somma-Vesuvius. The ash is called, generically, pozzolana, independently of its main use [trans. note: pozzolana comes from the word pozzo— a well], that of furnishing, together with calcium hydrate, water-resistant mortar; thus, in local terminology, ash and pozzolana are synonyms.

A local distinction is made only between Flegrean pozzolana (called,simply, “pozzolana”) and that which comes from Vesuvius (called pozzolana di fuoco [fiery pozzolana]). There is a substantial difference between the two types of pozzolana. The Flegrean variety is glassyand frothy with only a secondary amount of crystalline fragments
(especially Sanidine); fiery pozzolana, on the other hand, is characterized by a prevalence of crystalline fragments (mostly leucite) with little glassy substance. Furthermore, Flegrean pozzolanas have not been disturbed (at least those that are actually used as pozzolana), while Vesuvian pozzolana has been frequently disturbed and moved by rainwater. Accurate terminology would require that “pozzolana” be reserved for those cineritic materials with hydraulic reactivity, thus reacting with calcium hydroxide in water. That reaction is, in fact, termed a“pozzolanic” property.

It has now been ascertained that only some cineritic material of Flegrean origin displays pozzolanic properties, which derives from its essentially vitreous state, from the chemical composition and from the fine frothy texture. Ash of Vesuvian origin, on the other hand, has pozzolanic properties only rarely, and that is not so much due to the chemical composition as it is to the scarcity of materials in a vitreous state. Experience from Parravano and Caglioti, thirty years ago, showed that melting Vesuvian ash (inactive) (tempering it such that ittakes on a glassy, spongy state) and then pulverizing it produces pozzolana that reacts very well with calcium hydroxide.

As far as the granulometry of these materials is concerned, we should bear in mind that during an explosive eruption material ejected from the mouth of a volcano is very mixed as to form, size and density; it is only at a greater distance from the crater that the size and density of settled material can be classified. Generally speaking, the sorting process happens only with the heaviest and most voluminous products, the reason why volcanic ash is almost always a mixture of abundant small pumices and frequent lapideous lapilli and scoria. The texture and form of the single elements in this terrain depends strictly on the chemistry and conditions of the magma at the time of eruption as well as on the type of eruption; that is what determines the physical and mechanical properties.

This is especially true as regards porosity. The material can be very porous but still have particular characteristics due to the fact that only some of the pores are accessible, while some, depending on the nature of the frothy, bubbly texture, are very thin and isolated.

The angle of internal friction is  higher than in other loose sedimentary materials that were granulometrically the same. That depends on the markedly jagged form of the single elements. The tiny granules are so jagged that it leads one to think, in some cases, (particularly between 5mm and 0.05 mm—which includes most pozzolanas and pumices) that there must be an increase in the critical angle of repose as the granules get smaller. That is theopposite of what happens in loose sedimentary materials, where the critical angle of repose increases as the granules get bigger.

Finally we consider cohesion, a factor that seems to be of little importance in geotechnical laboratory tests, but which, in real life, should not be overlooked. Cohesion depends not so much on water content or degree of compaction as it does on the conditions when the material was formed. Cohesion increases if the materials settled hot and rich in volatiles (which would then cause partial diagenesis through autometamorphism). That is particularly true in those uniform and powerful pozzolana formations that settled rapidly after veryviolent closely-spaced explosive eruptions. We don’t notice this cohesion so much in laboratory tests because it is destroyed during core-sampling or during the preparation of the samples; we do notice the cohesion, however, on site. We have also noticed that the same materials, if they have been disturbed atmospherically, do not display the same cohesion even if they are more densely packed.

DISTURBED MATERIALS 

We said at the outset that classification of disturbed pyroclastic materials has to be based on granulometery. It is, however, still important to determine the genesis of these materials; that gives useful information as to the physical and mechanical characteristics of the materials as well as to their position in the surrounding terrain. In fact, if loose pyroclastic materials are disturbed, the mass of material can be modified not only in granulometric assortment and
petrographic composition of the entire mass, but the individual components, themselves, can undergo change. These changes will be a function of the length and intensity of the disturbance, and the mechanical and physical characteristics of the disturbed materials can wind up being notably different from the characteristics of the original,
undisturbed materials.

It is, thus, useful to know the nature of the disturbance that the materials are subject to. As a typical case in point, we look at littoral marine deposits, where we find a gravitative and mechanical selection of the finest and lightest materials and the destruction of the most fragile elements. This causes an enrichment of the heaviest and most resistant elements (lava pebbles, lapideous lapilli or scoria, crystalline fragments. etc.) which always appear smooth or, at least, softened and rounded off.

Pinning down precisely where the disturbance and, above all, later sedimentation took place is also important in reconstructing the characteristics of how the materials are positioned. Thus, for example, we know that the stratification in alluvial deposits is lenticular and variable, both vertically and laterally, for which reason we can extrapolate data from perforations only within certain limits. On the other hand, deposits in a lake or marsh might still have a certain variation vertically but, generally, will be uniform horizontally (or at least the variations will more subtle and gradual), making extrapolations that much easier. Furthermore, especially in marshes, we can predict frequent layers of humus and even peat, which have notoriously bad mechanical characteristics. Investigations in this type of terrain have to go to a greater depth than elsewhere, possibly limiting the number of core perforations.

Recognizing and distinguishing among different types of disturbed pyroclastic materials in the terrain of Naples and environs is not always easy since it entails painstaking investigations using the very latest techniques of sedimentary petrography. Also, various types of deposits are often found alternating with one another depending on the changed conditions at the sites where they are found; that is, marine or littoral deposits may come after alluvial and marsh deposits, and vice versa. For those reasons, on the 10,000:1 scale geo-technical map of the urban area that follows in the next chapter, the disturbed materials are not indicated individually; they are all represented by a single symbol.

It goes without saying that disturbed materials also include the products of erosion, the atmosphere acting on rock, whether lavas or cement-like pyroclastic materials or the artificial accumulations produced by man. These last materials, at least in the urban area, represent a fair percentage of the disturbed materials, at least down to the first few meters below the surface. Of secondary importance are those disturbed material that are not of volcanic origin; they appear sporadically, mixed in with volcanic materials and come from sedimentation around the entire Campania basin.

While this chapter was going to press, there appeared in Vol. XVI, 1966-67 of the Atti dell’Accademia pontaniana a note by A. Scherilloand E. Franco entitled “Introduzione alla carta stratigrafica del suolo di Napoli” [Introduction to the Stratigraphy of the Soil of Naples]. The authors say that this is an introduction to a more complete work to appear shortly. They have shown a very simplified statigraphy, using the classical subdivision into the three periods proposed by De Lorenzo. That version has piperno at the base of the stratigraphic column together with grey tuff and stratified yellow tuff; then, in the second period, they have yellow Neapolitan tuff and, finally, in the third period, loose products, primarily pumices and pozzolanas.

There are some substantial differences between that stratigraphy and our own (which is the one reconstructed by Rittmann and his collaborators in 1949). Theirs considers piperno as coming before all eruptions of yellow tuff and excludes the presence of yellow tuff craters in the urban area. Yellow tuff is said to have come from an eruptive center at quite a distance from the urban center; there might be some craters in the urban area that result from eruptions after those that produced yellow tuff. The most likely candidate for that would be the so-called Chiaia volcano.

As far as the stratigraphic position of piperno is concerned, the presence of re-disgorged blocks of yellow tuff in the breccia museo, not to mention the appearance of various piperno borders interlaced in the yellow tuff (for example, the piperno at via Palizzi) should be enough to prove that there are banks of yellow tuff below the piperno. As for yellow tuff volcanoes, it seems to us that at least the Chiaia volcano should be considered one of those, and we, too, think that there are still stratified yellow tuff volcanoes in the urban area that have not been discovered.

In any event, we await the appearance of the more detailed study announced by the authors, so that we may better compare their ideas to our own. We shall be quite content over the ideas that we share, since that means we have all taken another step towards understanding the subsoil of Naples.

END OF PART TWO, CHAPTER ONE

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