476 GEOLOGY OF THE DENVER BASIN. 



beds occur just below the Atlantosaurus series near the Black Hills and at 

 other points in the north, it is possible that they may be represented in the 

 same position in the Denver region. A typical exposure of the Baptanodon 

 beds may be seen near Lake Como, Wyoming', where the writer, in 1868, 

 lirst recognized this horizon and determined its Jurassic age. 



ATLANTOSAllUS BEDS. 



The most important geological horizon in the Denver region is the 

 Atlantosaurus beds, which are here extensively developed. They may be 

 seen to good advantage in passing- from Golden to Morrison, where they 

 will be found as a series of shales and sandstones resting' below either upon- 

 the red sandstone already mentioned or the succeeding' strata, and covered 

 above by the characteristic white Dakota sandstone, which in many places 

 has protected them from erosion. These Atlantosaurus beds are of fresh- 

 water origin, and their softer portions have suffered great denudation, thus 

 leaving extensive valleys. This horizon is one of the most distinct and 

 important yet found in this country, and it has now been traced, mainly by 

 the bones of the gigantic reptiles it contains, for about 500 miles along' the 

 eastern flank of the Rocky Mountains. In the vicinity of Denver these 

 deposits are gnu or ash colored, while both to the north and smith, and 

 especially west of the mountains, they are usually variegated in color, red 

 and yellow tints predominating. To the south of Denver the Atlantosaurus 

 beds may be seen at various points for a hundred miles and more — at the 

 Garden of the Cods, also near Canyon, and still farther south, at Webster 

 Park, beyond the Arkansas River. The main Oil Creek locality, about 14 

 miles north of Canyon, known locally as the "Bone Yard," has long - been 

 famous, as here and in the surrounding- region were found some of the 

 most remarkable fossils of this horizon. These remains, and others from 

 near Morrison, in the Denver Basin, will be discussed more fully later in 

 the present chapter. 



CRETACEOUS. 

 PTERAKODON BEOS. 



In the Dakota sandstone of Cretaceous age, next above the Atlanto- 

 saurus beds, only a tew fragments of vertebrate remains have yet been 

 discovered, and these beyond the limits of the Denver Basin; hence they 



