166 NEWER PLIOCENE STRATA. [Ch. XIII. 



Newer Pliocene Strata of Sicily. — In no part of Europe are tlie N'ewer 

 Pliocene formations seen to enter so largely into the structure of the 

 earth's crust, or to rise to such heights above the level of the sea, as in 

 Sicily. They cover nearly half the island, and near its centre, at Cas- 

 trogiovanni, they reach an elevation of 3000 feet. They consist princi- 

 pally of two divisions, the upper calcareous, the lower argillaceous, both 

 of which may be seen at Syracuse, Girgenti, and Castrogiovanni. 



According to Philippi, to whom we are indebted for the best account 

 of the tertiary shells of this island, thirty-five species out of one hundred 

 and twenty-four obtained from the beds in central Sicily are extinct. Of 

 the remainder, which still live, five species are no longer inhabitants of 

 the Mediterranean. When I visited Sicily in 1828 I estimated the pro- 

 portion of living species as somewhat greater, partly because I con- 

 founded with the tertiary formation of central Sicily the strata at the 

 base of Etna, and some other localities, where the fossils are now proved 

 to agree entirely with the present Mediterranean fauna. 



Philippi came to the conclusion, that in Sicily there is a gradual pas- 

 sage from beds containing TO per cent, of recent shells, to those in which 

 the whole of the fossils are identical with recent species ; but his tables 

 appear scarcely to bear out so important a generalization, several of the 

 places cited by him in confirmation having as yet furnished no more 

 than twenty or thirty species of testacea. The Sicilian beds in question 

 probably belong to about the same period as the Norwich Crag, although 

 a geologist, accustomed to see nearly all the Pleistocene formations in 

 the north of Europe occupying low grounds and very incoherent in tex- 

 ture, is naturally surprised to- behold formations of the same age so solid 

 and stony, of such thickness, and attaining so great an elevation above 

 the level of the sea. 



The upper or calcareous member of this group in Sicily consists in 

 some places of a yellowish-white stone, like the calcaire grossier of Paris, 

 in others, of a rock nearly as compact as marble. Its aggregate thick- 

 ness amounts sometimes to 700 or 800 feet. It usually occurs in regular 

 horizontal beds, and is occasionally intersected by deep valleys, such as 

 those of Sortino and Pentalica, in which are numerous caverns. The 

 fossils are in every stage of preservation, from shells retaining portions 

 of their animal matter and color, to others which are mere casts. 



The limestone passes downwards into a sandstone and conglomerate, 

 below which is clay and blue marl, like that of the Subappenine hills, 

 from which perfect shells and corals may be disengaged. The clay 

 sometimes alternates with yellow sand. 



South of the plain of Catania is a region in which the tertiary beds 

 are intermixed with volcanic matter, which has been for the most part 

 the product of submarine eruptions. It appears that, while the clay, 

 sand, and yellow limestone before mentioned were in course of deposition 

 at the bottom of the sea, volcanoes burst out beneath the waters, like that 

 of Graham Island, in 1831, and these explosions recurred again and again 

 at distant intervals of time. Volcanic ashes and sand were showered 



