PHYSICAL AND CLIMATAL CONDITIONS. 123 



" Mr. Belt, in an interesting paper (Quart. Journ. Oeol. 

 Soc, Nov., 1874), deals with similar ditticiilties in exi)lain- 

 ing tlie glaciation of Siberia. The nortliern jiart of Asia 

 appears in many ways to reseml)le tliat of America ; 

 surrounded l)y mountain-ehains on all sides save the 

 north, it is a sort of interior continental l)asin covered 

 witli 'vast level sheets of sand and loam.' As in the 

 interior regions of America, marine shells are absent, or 

 are only found along the low ground of the northern 

 coast. To account for tiiese facts, Mr. l>elt resorts to a 

 theory first suggested l)y him eight years ago, l)y whicii 

 he supj)oses the existence of a j)olar ice-sheet capable of 

 blocking up the entire northern front of the country, and 

 damming back its waters to form an immense fresh-water 

 lake. The outfall of this lake, during its highest stage, 

 lie supposes to have l)een through the depression l)etween 

 the southern termination of the Ourals and the western 

 end of tiie Altai to the Aral and Cas[»ian seas." 



Tlie main dilHculty in the way of this masterly ex- 

 planation is the great heiglit above the sea of the western 

 part of the plains; but this is now met by the ])rol)ability 

 of the depression of the plains contemporaneously witii 

 the elevation of the Cordillera, since suggested by the 

 author of the extract. To the absence of marine shells 

 from the deposits of the plains no importance need be 

 attached. The water may have been cold and brackish, 

 and in all gefdogical periods gravels, sands and conglom- 

 erates usually have few marine fossils. 



In 188;3 I had an opportunity of going over the same 

 ground, and my notes resi)ecting it are as follows : * 



The Cireat ]\Iissouri coteau to which Dr. (1. j\I. 

 Dawson first directed prominent attention as a glacial 



* s 



See Journal Geol. Society of London, 1883. 



