250 DESCRIPTIVE GEOLOGY. 



(Limnosaurus dpJiodon, Marsh. 



Crocodilians < Crocodilus JEUiotti, Leidy. 



^ Crocodilus hrevicoUis, Marsh. 



(Glyptosaurus princeps, Marsh. 



Lizards < Thinosaurus leptodus, Marsh. 



( Oreosaurus lentus, Marsh. 



(Boavus occidentalism Marsh. 

 Ophidians . . . . , iLithophis Sargenti, Marsh. 

 (^Limnophis crassus, Marsh. 



-ni. 1 ( Amia Newherrianus, Marsh. 



J ishes - - - { ^ _ , , , ' , 



(Lepidosteus glaber, Marsh. 



Cretaceous Uplift of Oyster Ridge. — Along the northwestern bor- 

 der of the Bridger Basin rises a series of low ridges, outliers of the Aspen 

 Plateau, which forms the watershed between the waters of the Green and 

 Bear Rivers. This line of elevation has been determined by a folding of 

 the Cretaceous and underlying strata at the time of the main pre-Cretaceous 

 uplift, and, as might naturally be expected from their position in the angle 

 of the great Wahsatch and Uinta Ranges, the direction of the fold shows 

 the combined influence of these two great shore-lines, whose waves some- 

 times cross, each preserving their independent strike, but in general take a 

 direction which is the resultant of the two. Over the upturned edges of 

 these folds, the beds of the Vermillion Creek Eocene have been deposited 

 unconformably, here consisting of a series of coarse argillaceous sandstones, 

 of banded chocolate and pinkish colors. The principal exposures of the 

 Cretaceous beds are found where the erosion of the Tertiaries has been 

 most considerable, viz, along the north and south valley of the Upper Little 

 Muddy and Ham's Forks, and in the ridge which bounds it on the east, 

 called, from the abundance of fossil remains of the genus Ostrea found upon 

 it. Oyster Ridge, whose culminating point, Ham's Hill, rises about 1,600 

 feet above the adjoining plains. The strikes of the beds vary from north 

 •30° east to due north, while their dip is in general to the westward; it is 

 evident, therefore, that a very considerable amount of erosion took place 

 between the time of the folding of these beds and the deposition of the over- 

 lying Tertiaries, probably combined with some faulting, in consequence of 



