40 Upham — Review of the Quaternary Era, 



envelopment of the land with an ice-sheet, which extended on 

 the Ohio and the Mississippi to the extreme southern limit of 

 the till and glacial striae. But in the Great Basin and Sierra 

 Nevada region early Quaternary events, according to LeConte 

 and Diller, were the formation of immense faults, by which 

 the mountain ranges were upheaved, the turning aside of 

 rivers from their former courses, and the outpouring of las^as, 

 which are often found capping the old auriferous river gravels.* 

 In the long interglacial epoch of the northeastern area, the 

 Sierra Nevada and Great Basin ranges were undergoing erosion 

 at a far more rapid rate than the valleys of the eastern rivers ; 

 and to this time we must assign the accumulation of the 

 greater part of the very thick alluvial deposits of the arid 

 region, which are called " adobe " and compared with the loess 

 of China by Russell. 



The ensuing second Glacial epoch, with a southward ad- 

 vance of the ice on the Atlantic coast beyond that of the 

 earlier glaciation, was probably induced by a geologically 

 sudden, high uplift of the northeastern part of the continent ; 

 and in the Upper Mississippi region, according to Chamberlin 

 and Salisbury, the differential elevation, increasing from south 

 to north, was 800 or 1000 feet. As an uplift of the continental 

 plateau, but without much disturbance of its mountain ranges 

 and of the general contour of the great interior area, this 

 movement appears to have embraced the entire width of the 

 country, raising the Rocky, Sierra Nevada, and Cascade moun- 

 tains to such altitude that large tracts became covered by 

 glaciers. 



Influenced by the changed climatic conditions, with increase 

 in the precipitation of snow and rain, and decrease in the rate 

 of evaporation, many enclosed basins of the arid region, which 

 had previously been dry or only occupied by shallow lakes, 

 became tilled almost or quite to overflowing. Two of these 

 Quaternary lakes, especially important because of their size, 

 namely, Bonneville in Utah and Lahontan in Nevada, have 

 been described respectively by Gilbert and Russell in mono- 

 graphs of the U. S. Geological Survey. Each of these lakes is 

 found to have a history of two epochs of humidity, with great 

 rise of their waters, divided by a very dry epoch, in which 

 they were lowered by evaporation until little or no water 

 remained. These lacustrine and interlacustrine stages in the 

 Great Basin do not appear, however, to represent the first and 

 second Glacial epochs of the northeastern states, with their 

 interglacial epoch ; but, as indicated by their place in the 

 sequence of Quaternary events, they seem referable to the 



* This Journal, III, vol. xxxii, pp. 167-181, Sept., 1886, and vol. xxxviii, pp. 

 257-263, Oct., 1889. U. S. Geol. Survey, Eighth Annual Report, pp. 428-432. 



