THE EOCENE OF NORTH AMERICA 467 



region was greater in the southwestern part than in the north- 

 eastern part. 



THE ORIGIN OF THE SO-CALLED LAKE DEPOSITS 



The stratified deposits of the Wasatch, Bridger, Uinta, and 

 others of like nature have been regarded and referred to as 

 lake deposits. Dutton seems to have been the first to recognize 

 and to point out the fact that some of them are not of lacustrine 

 origin. As early as 1880, in his report on the High Plateaus of 

 Utah he says : * 



There is another class of conglomerates which claims our special attention. 

 These are of alluvial origin, formed, not beneath the surface of the sea nor 

 of lakes, but on the land itself. They do not seem to have received from 



investigators all the attention and study which they merit Throughout 



great portions of the Rocky Mountain region they are accumulating today 

 upon a grand scale and have accumulated very extensively in the past. 



He then describes the formation and coalescence of alluvial 

 cones containing well-stratified material. Yet this idea of 

 subaerial deposition seems not to have been further emphasized 

 either by Dutton or by others. For a little later he writes 2 

 "The whole region [High Plateau], with the exception of the 

 mountain platforms and preexisting mainlands, has passed 

 through this lucastrine stage." 



In 1896 Gilbert 3 clearly interpreted certain stratified deposits 

 of Colorado as fluviatile. He speaks thus of the Upland sands 

 and gravels of the Arkansas River basin : 



Whatever the cause the streams which flowed from the mountains onto the 

 plains, and thence eastward across the plains, ceased to carve valleys in the 

 region of the plains, and began to deposit sediment. When they had filled 

 their channels so that their beds lay higher than the neighboring country, they 

 broke through their banks, shifting their courses to new positions and they 

 then came to flow in succession over all parts of the plains, and to distribute 

 their deposits widely, so that the whole plain of the district here described 

 was covered by sands and gravels brought from the canyons and valleys of 

 the Rocky Mountains. 



'Geol. of the High Plateaus of Utah, pp. 219 et seq., 1880. 



2 The Grand Canyon of the Colorado, p. 216, 1882. 



3 Seventeenth Ann. Rep. U. S. Geol. Surv. for 1895-6, Part II, pp. 575, 576. 



