750 GEOLOGY. 



numberless as are the glories of the firmament." The composition of the polishing slate 

 of Bilin is far from being unique ; for in several other European localities, and very 

 largely in America, strata consisting mainly of fossil animalcules have been observed. 

 This is the case with some siliceous marls belonging either to the ancient or to the median 

 tertiary era, which have a total thickness of twenty feet, and spread out to a considerable 

 distance, upon which the town of Richmond, in the state of Virginia, is built. 



3. Pliocene period, or Modern Tertiary Strata. Deposits are included in this division, 

 in which the fossil shells are largely identical with living species ; but this much more 

 strongly applies to some members of the group than to others, and hence the subdivision of 

 pliocene strata into older and newer. A great part of the sub-appenine range in Italy 

 belongs to the older, whose shells were observed by Lamarck to differ from those of the 

 Paris basin, and to have a considerable proportion agreeing with species now living in 

 the Mediterranean or in the seas of tropical climates. The sub-apennine hills rise to the 

 height of .from one to two thousand feet, and extend along the 

 main chain of the Apennines, which are composed of secondary 

 rocks, both on the Mediterranean and Adriatic sides. They 

 consist of marls, sands, clays, and calcareous tufa, generally 

 of marine origin. By dredging the bed of the Adriatic, it 

 Murex aiveoiatus. has been ascertained that depositions are now forming there, 



whose lithological character closely resembles that of the sub-apennine tertiaries. 

 There can be no doubt of the formation of the latter from the waste of the central 

 mountains of the peninsula, when the sea flowed up to their base, depositing their 

 detritus in its bed through a long course of ages, subterranean forces raising the 

 strata at various intervals to their present elevation. Testaceous fishes and marine 

 plants, now found imbedded in the hills, indicate their oceanic origin ; but another 

 class of deposits, containing fluviatile and lacustrine remains, intimate that, after the 

 ocean had retired, rivers and lakes held possession of parts of the vacated territory for a 

 time sufficient to produce the fresh-water beds, which alternate with marine, near the town 

 of Sienna, the sea re-entering its ancient haunt, and again retreating, in the course of 

 those various alterations of the level of the land from volcanic action, the monuments of 

 which are so striking in the Campagna di Roma. With the sub-appenines, in point of 

 age, some tertiaries in the Morea are classed, with patches in Spain, and the largely 

 developed provincial " crag " of Norfolk, Suffolk, and Essex, which overlies the London 

 clay in the latter county. The crag is a heterogeneous group of strata, in part lacustrine, 

 but chiefly marine, presenting among its fossils mammalian relics, teeth and bones of a 

 species of shark, an abundance of corals, and shells, among which, out of 111 species 

 examined by M. Deshayes, 66 were found to be extinct and 45 living, the latter, with 

 one exception, now the inhabitants of the German Ocean. 



A much greater approximation to the present state of things appears in Sicily, where 

 Mr. Lyell found that amid vast accumulations of marine shells, entering into the compo- 

 sition of mountains of no inconsiderable altitude, nearly all were specifically identical 

 with those now inhabiting the contiguous sea. These formations are therefore regarded 

 as belonging to the most modern tertiary group, or the newer division of pliocene strata. 

 The south of Etna is occupied by an extensive tract of limestone, marl, and sandstone, 

 connected with volcanic rocks, called the Val di Noto, in which the hills rise to the height 

 of from one to two thousand feet, composed of sedimentary strata and igneous products. 

 These are associated in such a manner as to show, by the stratified rocks overlying lava, 

 that during their deposition submarine igneous eruptions occurred at intervals in that 

 now active focus of volcanic action. Probably the formation of the fresh- water strata, 

 through which the beautiful Rhine passes in its course from Constance to Schaffhausen, 



