Geology of Russia. 77 



cene age cannot be distinguished from the Great Oolite of the 

 Jurassic period. 



These facts are most valuable, as shewing that at all pe- 

 riods sedimentary rocks were formed, as they must now be 

 forming, at the bottom of the sea, from the detritus of ad- 

 joining land, by the same agencies of disintegration as are 

 now at work ; and that then, as now, gravel, sand, and mud, 

 were the forms which such detritus must have taken, to be 

 afterwards compressed together, and consolidated by a va- 

 riety of causes acting more or less intensely in different situa- 

 tions. 



But Sir R. Murchidon also observes, that the connection 

 between the character^ of the fossils and the nature of the 

 matrix in which they are imbedded, is more pointedly brought 

 before the observer who ranges over the boundless tracts of 

 Russia, than in any other country which he has examined. 

 Notwithstanding the absence of violent dislocations, the va- 

 rious Russian formations, though horizontal, or so nearly so, 

 that they may be all considered conformable to each other, 

 are as distinctly separable by their included remains, as in 

 those typical and dislocated tracts where geologists first 

 worked out*their order. And these observations hold good 

 in the newer as well as in the older deposits ; thus, in the 

 regions of the Volga, greensand, ironsand, chalk, and chalk 

 marl occur, in which the same groups of fossils prevail as in 

 the rocks of Britain and France, which hold the same rela- 

 tive place in geological succession ; and pure white chalk, 

 containing some characteristic organic remains, extends from 

 the British Isles to the confines of Asia. 



That so vast a tract of country, unlike most other parts of 

 Europe, has been so little broken up locally by igneous erup- 

 tive rocks, may perhaps, with great probability, be ascribed 

 to this, that a safety-valve was opened, an enormous crack 

 or cleft was made on the east, by a subsidence of the coun- 

 try on the west, through which the pent-up elastic force and 

 the molten matter escaped, and thus the high pressure was 

 taken off from under the broad expanse. The Ural Moun- 

 tains, bounding Russia in Europe on the east, are a compa- 

 ratively narrow ridge, made up of igneous rocks and sedi- 



