§ 17. SILURIAN STRATA OF EUROPE AND AMERICA. 



781 



of their deposition, except by such gradual movements as 

 those by which large areas in Sweden and Greenland are 

 now slowly and insensibly rising above, or sinking below, 

 their former level.* 



In Russia, the lower division of the Silurian system is 

 characterized, as elsewhere, by the abundance of Orthes, 

 Leptamas, and other brachiopodous shells, Orthoceratites, 

 and Trilobites ; and the upper, by large masses of corals, 

 especially of Favosites, Catenipora, &c. ; and the Devonian 

 strata teem with remains of the typical species of fishes, and 

 Spirifers, Leptamae, and Serpulae (ante, p. 757). Through- 

 out the immense extent of Central Russia, forming nearly 

 one-half of the European continent, there are no intrusions 

 of igneous rocks ; and the whole of the deposits, from the 

 lowermost to the uppermost, are but little altered, and in 

 many instances are unsolidified; yet each group contains 

 the same characteristic organic remains as in England. 

 But in the Ural mountains and Siberia, the formations 

 of the same age are thrown up into mural masses, broken 

 into fragments, impregnated with mineral matter, and 

 exhibit every variety of metamorphic action. Yet a 

 clear distinction may nevertheless be drawn between these 



* Mr. Lyell's Elements of Geology, vol. ii. p. 175. On these phe 

 nomena Mr. Lyell thus comments : — " These facts are very important, 

 as the more ancient rocks are usually much disturbed, and horizon 

 tality is a common character of the newer strata. Similar exceptions, 

 however, occur in regard to the more modern or tertiary formations, 

 which, in some places, as in the Alps, are not only vertical, but in a 

 reversed position. These appearances accord best with the theory 

 which teaches, that, at all periods, some parts of the earth's crust have 

 been convulsed by violent movements, which have been sometimes 

 continued so long, or so often repeated, that the derangement has 

 become excessive : while other spaces have escaped again and again, 

 and have never once been visited by the same kind of movement. 

 Had paroxysmal convulsions ever agitated simultaneously the entire 

 crust of the earth, as some have imagined, the most ancient fossil- 

 iferous strata would nowhere have remained horizontal."' — Ibid. p. 176, 



