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Show viii PREFACE, obtained chiefly from the Italian strata; and as I had already conceived the idea of classing the different tertiary groups, by reference to the proportional number of recent species found fossil in each, I was at pains to learn what number Signor Bonelli had identified with living species, and the degree of precision with which such identifications could be made. With a view of illustrating this point, he showed us suites of shells common to the Subapennine beds and to the Mediterranean, pointing out that in some instances not only the ordinary type of the species, but even the different varieties had their counterparts both in the fossil and recent series. The same naturalist informed us that the fossil shells of the hill of the Superga, at Turin, differed as a group from those of Parma and other locali~ies of the Subapennitle beds of northern Italy; and, on the other hand, that the characteristic shells of the Su perga agreed with the species found at Bordeaux and other parts of the South of France. I was the more struck with this remark, as Mr. Murchison and myself had already inferred that the highlyinclined strata of the Valley of the Bormida, which agree with those of the Superga, were older than the more horizontal Subapennine marls, by which the plains of the Tanaro and the Po are skirted. When we had explored some parts of the Vicentin together, Mr. Murchison re-crossed the Alps, while I directed my course to the south of Italy, first staying PREFACE. ix at Parma, where I studied, in the cabinets of Signor Guidotti, a beautiful collection of Italian tertiary shells, consisting of more than I 000 species, many of which had been identified with living testacea. S_ignor Guidotti had not examined his fossils with reference to their bearing on geological questions, but computed, on a loose estimate, that there were about 30 per cent. of living species in the Subapennine beds. I then visited Florence, Sienna, and Rome, and the results of my inquiries respecting the tertiary strata of those territories will be found partly in the body of the work, and partly in the catalogues given in Appendix II. On my arrival at Naples I became acquainted with Signor 0. G. Costa, who had examined the fossil shells of Otranto and Calabria, and had collected many recent testacea from the seas surrounding the Calabrian coasts. His comparison of the fossil and living species had led him to a very different result in regard to the southern extremity of Italy, from that to which Signors Guidotti and Bonelli had arrived in regard to the north, for he was of opinion that few of the tertiary shells were of extinct species. In confirmation of this view, he showed me a suite of fossil shells from the territory of Otranto, in which nearly all the species were recent. In October, 1828, I examined Ischia, and obtained from the strata of that island the fossil shells named in Appendix II., p. 57. They were all, with two or |