THE CENOZOIO GKOUPS. 171 



storm, I am not willing 1 to disregard explanations so obvious and so certain 

 for an extraordinary and more violent hypothesis. 



Irregular accumulations of clay, accumulations of sand, of gravels, and 

 bowlders having in a general way all the lithologic characteristics of "drift" 

 are very common in the Rocky Mountain region, and in many cases I am 

 convinced that their origin can be traced to ordinary atmospheric agencies 

 acting on the adjacent hills and mountains; and no glaciers or icebergs are 

 needed for their explanation. 



Nor need the thickness and extent of this Bishop Mountain Conglomer- 

 ate serve to weaken this explanation, for the sub-aerial gravels in the valleys 

 between the ranges in the Basin Province are of equal and often of greater 

 development. Whenever a low plain, valley or basin is for a comparatively 

 long period but little elevated above the base level of erosion, and during 

 this time mountains and hills stand about the lowlands, there must be a great 

 accumulation of drift, and where the highlands are areas of progressive ele- 

 vation and the lowlands areas of progressive subsidence this accumulation 

 may continue indefinitely. 



Thus it is that I attribute the drift of the Rocky Mountain region to 

 sub-aerial agencies, chiefly the action of rains and streams. Mountains are 

 not degraded by the slow washing down of their surfaces but they are dug 

 down by the corrasion of deep channels and the undermining of ledges and 

 cliffs, and the materials thus loosened from the great rock masses to which 

 they originally belonged are carried down to the lowlands by storms. In 

 one hour of storm more material is carried to the lowlands than in days, 

 weeks, or months when the mountain streams are clear brooks. Yet there 

 has been glacial action in the Uinta Mountains, for there are found undoubted 



MORAINAL DEPOSITS. 



* 



The deep valleys that lie at the feet of the axial peaks of this great 

 range have been beds of now extinct glaciers. Morainal deposits, roches 

 moutonneeSj glaciated grooves, and morainal lakelets are found in very 

 many of these elevated valleys. Often the valleys are so choked with the 

 materials thus accumulated by the action of ice that travel across them is of 

 great difficulty. From the crevices between these ice piled rocks high pine? 



