196 BULLETIN UNITED STATES GEOLOGICAL SUEVEY. [Tol.Y. 



Group are observed to rise gently as the Wyoming Mountains are 

 approached. The Wyoming Mountains extend north and south in lon- 

 gitude 110° 48'. Before they are reached, however, we come to an anti- 

 clinal fold, which forms a ridge that is apiDroximately parallel to the 

 mountains and about six miles east of them. This fold, named Meridian 

 Fold, marks the rim of Green Eiver Basin in this region, and is composed 

 of Jurassic and Cretaceous strata. Between the ridge thus formed and 

 the Wyoming Mountains there is a depressed area named Meridional 

 Valley, in which there is a series of gray and greenish sandstones and 

 shales resting conformably upon the Cretaceous beds. They are several 

 thousand feet in thickness and dip to the westward, abutting against the 

 westward-dipping Carboniferous limestones of the Wyoming Eange. 

 The junction marks the line of a fault of some 2,000 or 3,000 feet, the 

 downthrow being on the east. At two points only were fossils found 

 along the west side of the Green Eiver Basin. The following were 

 recognized : 



Cam^eloma macrospira. 



Fyrgulifera sp.? 



Corhula sp. 1 



Few as they are, they are sufficient to warrant the reference of the 

 beds from which they were obtained to the Laramie Groui). The Line of 

 junction of the Laramie sandstones and the Carboniferous limestones 

 is generally obscured by the debris, but at several places the contact 

 was so well seen as to leave no doubt of its being a fault, and not a line 

 marking the ancient shore-line of the Laramie Sea. There was also no 

 evidence in the sandstones of the immediate proximity of a shore-line 

 during their deposition, as there was in the beds of the Wahsatch Group. 

 The line of the fault does not extend in a straight line along the eastern 

 front of the range ; but the Laramie sandstones fill bay-hke recesses in 

 the range. This is especially the case towards the north, and led me at 

 first to think that the range had formed a part of the shore-line of the 

 Laramie Sea. 



In the northern iiart of Meridional Valley, fragments of the Wahsatch 

 Group are seen resting unconformably on the Laramie sandstones, and 

 continuing also over the ends of the Cretaceous strata, although usually 

 the Wahsatch Group does not extend west of the Meridian fold, where 

 it is seen resting on the uptui-ned edges of Jurassic and Cretaceous strata. 

 The Green Eiver Group does not usually reach the summit of the ridge, 

 seeming to have been eroded away as the beds were uplifted to form its 

 eastern slopes, and now it forms bluffs facing the ridge just as the place 

 of greater inclination is reached. 



The portion of the Wahsatch Group restmg on the older beds proba- 

 bly represents only the upper part of the group, and has a thickness of 

 only 700 or 800 feet. Its conglomerates contain pebbles of Carbonifer- 

 ous limestone, evidently derived from the adjacent Wyoming Eange. 

 It is evident, therefore, that precedent to the deposition of these beds 



