882 HISTORICAL GEOLOGY. 



and at one place on the Banks of Newfoundland. Their absence from the 

 coast region in the higher latitude may be owing, as generally believed, to 

 the present submergence of the border on which such beds were deposited. 

 But the existence, for the most part, of rapidly deepening waters north of 

 Newfoundland, and the denuding power of the waves of the open ocean may 

 have been the effective cause along much of the coast. 



Although the ocean had been excluded from tlie Continental Interior at 

 the close of the Cretaceous period, rock-making was still carried forward over 

 much of its area by means of vast freshwater lakes. These lakes had their 

 Fishes and other aquatic life, and their borders were frequented by various 

 animals of the land, including Mammals of many species, with various small 

 Reptiles, and the remains of these species abound in the lacustrine deposits. 

 The freshwater Tertiary formations have consequently an importance not 

 inferior to that of the marine beds. 



The great lakes of the earlier Tertiary — the Eocene — were situated in 

 the Rocky Summit region, within the United States, mostly over the area of 

 the Laramide mountain system. One Eocene lake, the Wasatch (W on the 

 map), covered a large region north of the Uinta Mountains, between the 

 parallels of 40° and 44°, including parts of Utah, Wyoming, and a portion of 

 northwestern Colorado ; and as the earlier Wasatch Lake narrowed its limits 

 in the later Eocene, it became the Bridger Lake. The " Green River basin" 

 was part of the Wasatch. Another, the Uinta Lake (U), lay south of the 

 Uinta Mountains, chiefly within the boundaries of Utah. Another smaller 

 lake, the Puerco (P), was situated in the northern part of New Mexico, and 

 extended across the border into Colorado. Two others, of small size, were 

 situated in the region of the Great Basin west of Great Salt Lake. 



The lacustrine beds of Wasatch Lake occupy a plateau region about 6500 

 feet (6000 to 7000) above the sea level. The height of the village of Green 

 River, within the former, above tide level, is 6140 feet ; of Bridger, 6780 feet j 

 of Wasatch, 6789 feet. 



Nearly all the latei' Tertiary lake basins lie either to the east or west of 

 the Summit region, over Nebraska and the adjoining states on the eastern 

 slope of the Rocky Mountains, or between nearly the same parallels but 

 farther west ; part of them in the Oregon and Nevada portions of the Great 

 Basin region. The extent of the Eocene lakes over the Summit region is 

 regarded as evidence that the general mass of the mountains at the time 

 stood but little above the sea level. The great thickness which the beds 

 attained in the course of the Eocene is proof that the areas were undergoing 

 a slow subsidence, keeping pace with the deposition, while their borders were 

 essentially stable ; and that the position of the area of maximum subsidence 

 changed in the course of the Eocene period. Further, the position and great 

 extent of the Miocene lakes, covering a large part of the eastern slope of the 

 mountains, are evidence that the elevation which took place at the close of 

 the Eocene, draining the lake basin, was small. 



All the land of the Tertiary continent had its working streams and 



