Earth-Movements in the Bay of Naples Author(S): R
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Earth-Movements in the Bay of Naples Author(s): R. T. Günther Source: The Geographical Journal, Vol. 22, No. 2 (Aug., 1903), pp. 121-149 Published by: The Royal Geographical Society (with the Institute of British Geographers) Stable URL: http://www.jstor.org/stable/1775606 . Accessed: 14/01/2015 06:56 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The Royal Geographical Society (with the Institute of British Geographers) is collaborating with JSTOR to digitize, preserve and extend access to The Geographical Journal. http://www.jstor.org This content downloaded from 128.235.251.160 on Wed, 14 Jan 2015 06:56:06 AM All use subject to JSTOR Terms and Conditions The GeographicalJournal. No. 2. AUGUST, 1903. VOL. XXII. EARTH-MOVEMENTSIN THE BAY OF NAPLES.* By R. T. GIUNTHER, M.A., F.R.G.S., Fellow of Magdalen College, Oxford. "Jacent in litore sedificiorum fragmenta qute romanam maiestatem praeseferunt, abierunt in scopulos crustatis piscium generibus habitatos."-Capaccio, ' Hist. Neap.,' cap. xiv. 1607. IN a preliminary note read at the Bradford Meeting of the British Association in 1900, it was suggested that the ancient ruins in the sea along the Neapolitan shore might yield satisfactory information regard- ing the Roman coast-line of the Phlegrnean Fields. With this view a new survey of parts of the coast was prepared and an interim report was laid before the 1901 Meeting by the Committee on " the changes of the land-level of the Phlegraean Fields." We hope that, by describing the more noteworthy geogiaphical results, a light may be thrown on some vexed problems and may tend to elucidate them. Babbage and others have shown that the burrows of marine shell-fish in the columns of the Temple of Serapis, at a height of about 19 feet above sea-level, bear witness to a subsidence followed by an elevation of the land through not less than this distance since the construction of the building. We have been able to collect supplementary evidence which indicates that since the Roman dominion the Neapolitan coast first sank about 35 feet, and then rose about 19 feet to slightly above its present level. Reasons will be given for believing that this great oscillatory movement was not of a seismic nature and confined to the immediate vicinity of a volcano, but affected so large an area that it must be regarded as of the order of those slow and majestic movements of the crust of the Earth which are now in progress in Sweden and elsewhere, by which continents have risen from the sea, and which can often only be detected by observa- tions spread over a long space of time. * Read at the Royal Geographical Society, February 9, 1903. Map, p. 236. No. I[.-AuGIJST, 1903.] K This content downloaded from 128.235.251.160 on Wed, 14 Jan 2015 06:56:06 AM All use subject to JSTOR Terms and Conditions 122 EARTH-MOVEMENTSIN THE BAY OF NAPLES. The assertion that the land-level in Roman times was about 16 feet higher than it is at present, depends partly upon the discovery of two submerged regions covered by the foundations of numerous houses, perhaps the forgotten site of Parthenope or Palespolis, with an ancient harbour and a coast roid, which are not without archaeological interest. To the authors whose works inspired and facilitated our labours, we would make most grateful acknowledgment. Without Lyell, Niccolini, Beloch and many another, we could have accomplished but little in the time at our disposal. We also thank our fellow-members of the British Association for their encouragement of the work, and H.B.M. Consul- General at Naples, Mr. E. Neville-Rolfe, for furthering our plans. I. CAPRI. Indications of changes in the level of the island of Capri are very numerous and clear, and many are of comparatively recent date. It is not proposed to discuss here that vast series of earth-movements which have resulted in the uprising of the Capriote Tertiary limestones from a horizontal position on the sea-bottom to the surface and higher, with a dip from south to north at angles varying from 25? to 70?. Concerning the details of these very ancient changes on a gigantic scale we have but scanty knowledge; they no doubt were in operation before the strata of Capri had become dislocated from those of an extensive limestone continent. Some of the evidence we are about to consider points to the long-continued existence of the island nearly in its present form. The most important evidence of relative levels of sea and land in former times is of three kinds. Firstly, marks of marine erosion, occurring either above or below the present sea-level; secondly, raised beaches, or beaches apparently collected by, but now beyond the reach of the waves; and, thirdly, submerged constructions, now standing at a lower level than that at which they were built. Marine Erosion at the Present Day.-The details of the process of erosion of limestone by the sea may be well studied at many places around the coast of Capri. Owing to the absence of a large tide in this part of the Mediterranean, the erosive action of the waves is nearly confined to one horizontal zone. In those parts of the island where the cliffs rise sheer from deep water, and are neither too much exposed to the fierce onslaught of storm waves, nor composed of rock of too friable a nature, there we find a groove chased horizontally along the face of the cliffs at the water-line. The size and depth of this groove varies with the hardness or exposure of the rock, but on the whole it is deepest at the mean tide-level. The most vigorous erosion, therefore, is taking place between wind and water. This content downloaded from 128.235.251.160 on Wed, 14 Jan 2015 06:56:06 AM All use subject to JSTOR Terms and Conditions EARTH-MOVEMENTSIN THE BAY OF NAPLES. 123 Immediately above and below the water-line, erosion is proceeding very slowly; above, partly on account of the absence of the eroding medium, partly on account of a protective coat of calcium carbonate dissolved from the rocks above and spread by a trickling film of spring water. In some places there is an organic growth forming a con- spicuous black band distant a foot or two from the water; this aloo seems to have a protective action. Beneath the surface of the water, but near enough to benefit by the foam of breaking waves, a garb of coralline and algal growth luxuriates, and protects the stone. The size and appearance of the narrow horizontal groove indicate that it is chiefly the result of steady erosionby solution in calmweather FIG. 1.-PARTIALLY ERODED BLOCK OF LIMESTONE. -........... riginal co, tour. Seawee:l. at the surface of the water. The cliffs of Capri tell us in clear geo- logical sign-language that the waves which dash up in storms can have taken but a small part in the etching of the groove. On the north side of the island calm has prevailed, and the grooving and undercutting are well marked; on the south, full exposure to the open sea has resulted in faster scaling from the face of the cliffs and in the obliteration of the groove of solution. When rain and spray fall on flat limestone surfaces near the sea- level, solution is very rapid. The result may be seen in all stages, on many a partially submerged rock and boulder on the north and east coasts. The process is indicated in the diagram, which was drawn from an actual block of limestone (Fig. 1). The dotted line represents the original contour of the block. The portion below water has nearly retainedits original dimensions,having been protected by a thick growth of alge. At the water-line there is a groove of solution all round the stone; and the upper surface, which is undergoing rapid disintegration by rain and spray, is jagged and uncomfortableto walk upon. Soon all will be planed down to low-water mark, and then the kindly covering of weeds will hinder further destruction. K2 This content downloaded from 128.235.251.160 on Wed, 14 Jan 2015 06:56:06 AM All use subject to JSTOR Terms and Conditions 124 EARTH-MOVEMENTSIN THE BAY OF NAPLES. The furrow at the present water-level runs in and out of the older caves and cavities like a hollow moulding round the recesses of a build- ing, and may be traced almost all round the island in the less exposed parts. This furrow is rarely more than a foot in depth; but where natural cracks or soft places in the rocks have favoured, the erosive action has been more extensive, and deeper hollows and little caves have been scooped out. The Upper Erosion-line.-Similar marks of erosion occur at other levels above the surface of the sea. In some places they are as clear as if they had been cut yesterday, in others they have become almost covered up by newly deposited stalactitic matter; in the moreweathered parts they have been entirely obliterated.