184? PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



They extend from the plains of Prussia to the frontiers of Asia on 

 the east, and to the Frozen Ocean on the north. They are moreover 

 seen to underlie the cretaceous and tertiary deposits of Southern 

 Russia, and appear in the steppes which lead from Europe into 

 Asia ; but in these southern regions they undergo a change in litho- 

 logical characters, becoming siliceous and calcareous grits, and re- 

 sembling the conglomerates and grits found at the base of the oolitic 

 series in some parts of England ; their fossil contents however con- 

 tinue the same. 



Cretaceous Rocks, 



These occupy a great part of Southern Russia, but are unknown 

 to the north of 55^^ of latitude. In regard to mineral arrange- 

 ment, there exists that sort of general parallelism between the beds 

 in Russia and those in Western Europe, particularly with those of 

 Eastern Germany, which we might expect to find in strata of the 

 same epoch separated from each other by great distances. Green- 

 sand, ironsand, chalk and chalk marl occur, in which the same 

 groups of fossils prevail as in rocks of Britain and France which 

 occupy the same relative age in geological succession ; and pure 

 white chalk, containing some characteristic organic remains, occurs 

 at intervals to the confines of Asia. In the southern steppes of the 

 Don Cossacks, on the banks of the river Donetz, chalk possessing 

 all the characters of the English and French chalk, and containing 

 some of its characteristic fossils, occurs of great thickness, Artesian 

 wells having been sunk in it to a depth of 630 feet without any in- 

 dications of a change of rock. It contains layers of flint, and the 

 banks of the same river exhibit a section of a greensand group 

 seventy feet thick, resting upon an equivalent of our coral rag, and 

 surmounted by white chalk. A zone of true chalk, 120 miles in 

 width, stretches through a great region about 100 miles south-west 

 of Orenburg. 



The cretaceous rocks occupy a very limited zone on the eastern 

 side of the AUeghanies, extending about sixty miles, but having 

 rarely a breadth of half a mile. They sweep round the southern 

 extremity of these mountains, occupying a vast tract which stretches 

 far westward of the Mississippi ; and Mr. Lyell saw a collection of 

 chalk fossils brought by M. Nicollet from the higher parts of the 

 Missouri river. It appears further, from the recent report of Cap- 

 tain Fremont, that cretaceous rocks occur on the eastern flanks of 

 the Rocky Mountains. The series examined by Mr. Lyell in the 

 State of New Jersey consist of a lower portion of greensand and 

 green marl, and above these a pale yellow limestone with corals, 

 both however belonging, in the opinion of Mr. Lyell, who has care- 

 fully examined a large series of fossils, to the age of the white chalk, 

 including the period from the gault to the Maestricht beds. As a 

 detailed account of these beds and their fossil contents is given in 

 the first volume of the Society's Journal, I need not dwell further 

 upon them, except to give a statement of the general results. There 

 is a remarkable generic accordance between the fossil raollusca, 



