CHANGES OF THE SEA DUE TO ICE ACCUMULATION". 515 



latitude of the nimalayau range and the position of Thibet and MongoHa 

 in an arid and jiai'tly rainless beh, which stretches thence west to the 

 Sahara, forbade their ghxciation; but from these recently uplifted Asiatic 

 table-lands and mountains the most extensive Pleistocene stratified deposits 

 in the world have been brought down by rivers and spread in the vast low 

 plains of Siberia, eastern China, and northern India, sloping gently toward 

 the sea, into which the finer part of this alluvium is carried. All the puz- 

 zling features of the Cliinese loess formation,^ reaching to great elevations 

 with such thickness and slopes of its surface that it could not be so accumu- 

 lated as alluvium of flooded streams under the present conditions, seem to 

 be readily explained by referring its deposition to annual floods from 

 immense snow melting dm-iug the European and North American Glacial 

 period upon the gradually rising central part of the Asiatic continent, 

 which consists largely of easily erosible strata, and had in pre-Glacial time 

 become extensively disintegrated by weathering under a dry climate. 



EFFECTS OF ICE ACCUMULATION ON THE SEA-LEVEL. 



Dm'ing the Glacial period significant changes of the sea-level were 

 caused, first, by abstraction of water from the ocean and its deposition on 

 the land as snow, which under pressure made the vast ice-sheets; and, 

 second, by ice attraction of the ocean, lowering it still further, except in the 

 vicinity of glaciated lands. An area of about 4,000,000 square miles in 

 North America and another of about 2,000,000 square miles in Europe 

 were covered by ice-sheets, which in their maximum extent had probably 

 an average thickness of a half or two-thirds of a mile, or perhaps even of 1 

 mile. Disregarding the accumulation of ice-sheets of smaller extent, which 

 probably or possibly existed at the same time in parts of Asia and of the 

 southern hemisphere, as also the glaciers of mountain districts, the lowering 

 of the ocean surface, which covers approximately 145,000,000 square miles, 

 would slightly exceed 100 feet, if the mean depth of the ice accumulation 

 was a half mile. More probably the sea over the whole globe was thus 



'Baron Richthofen,Geol. Magazine (2), Vol. IX, 1882, pp. 293-305. J. D. Whitney, Am. Naturalist, 

 Vol. XI, pp. 705-713, Dec, 1877. R. Pumpelly, Am. Jour. Scl. (3), Vol. XVII, pp. 133-144, Feb., 1879. 

 E. W. Hilgard, Am. Jour. Sci. (3), Vol. XVIII, pp. 106-112, Aug., 1879. 



