GEOLOGICAL SUEVEY OF THE TEREITORIES. 457 



formation shows a gentle eastward clip, which causes it to pass under 

 another very similar series of strata, to which Dr. Hayden has applied 

 the name Washakie group. In the latter, so far as our present knowl- 

 edge extends, only fresh water and land types of fossils have yet been 

 fouud, and we have always regarded it as beiug of Tertiary age. Exactly 

 where the one ends and the other begins we did not see ; though the 

 Bitter Creek series certainly come eastward to division E of Br. Bannis- 

 ter's section, at Black Butte, as we found its characteristic molluscan 

 remains there in the same bed containing the reptilian bones. 



Between Black Butte and Bitter Creek Stations (separated by a dis- 

 tance of only about six miles by a right line east and west) we ob- 

 served no marked change of lithological characters, from the Bitter 

 Creek series to the Washakie group, while the two series vseemed to be 

 conformable in dip. Although our observations in this interval were 

 too limited to warrant a positive opinion on that point, we left Black 

 Butte Station under the impression that the brackish-water types of the 

 Bitter Creek series probably extend little, if any, higher in the series, 

 or farther eastward, than the tops of the hills near Black Butte. 



At Salt Wells station, which is situated in an anticliilal, owing to the 

 rising of the strata, as we come westward, (see Dr. Bannister's section,) 

 a lower series of rocks comes up from beneath the Bitter Creek beds. 

 This lower group consists of thin layers of grayish and drab slabby 

 sandstones, and shales with, at places, some appearances of coal in the 

 upper part. It seems to be conformable with the Bitter Creek series, 

 and probably belongs to the Cretaceous, though we saw no fossils in it. 

 Erom exposures seen near Salt Wells, there would appear to be 700 to 

 possibly 1,000 feet of these lower rocks here, above the valley. 



In going westward from Salt Wells station we soon observe a reverse 

 of dip, and the Bitter Creek beds again appear, dipping westward or 

 northwestward. At, and near Kock Springs, extensive coal-beds occur 

 in this formation, and here we found associated with or near one of these 

 beds the fresh, brackish, and salt-water types of shells already men- 

 tioned. The dip of the strata here is to the northwestward, at an angle 

 of 10° to 12c> below the horizon, so that a short distance farther west 

 the whole group passes under a great series of whitish, greenish, and 

 at places reddish laminated clay of Tertiary age, forming Dr. Hayden's 

 Green Eiver group, and rising into hills 700 to 800 feet in height above 

 the valley. The strata of this latter group are distinctly unconformable 

 to those of the Bitter Creek series, their dip being only 2° to 3° west- 

 ward. 



But, returning to the question respecting the age of this Bitter Creek 

 series, it may be stated, in the first place, that Mr. Emmons evidently 

 regarded it as Cretaceous, as may be seen from his remarks in Mr. 

 King's report, iDublished in 1870 ; while Dr. Hayden favored the conclu- 

 sion that it is a marine Tertiary group, or a transition series between 

 the Tertiary and Cretaceous, in his reports of that and the following 

 years. 



The only fossils I had ever seen from this formation, previous to vis- 

 iting the region during the past summer, were two species of Ostrea 

 and one of Anomia from Point of Eocks; and two shells, one, or possi- 

 bly both, related to Corhicnia, from Hallville. Those from Point of 

 Eocks I referred to the Cretaceous, placing them in the Cretaceous list, 

 in Dr. Hayden's report of 1871. This I did, mainly because there were 

 among them no fresh-water, or strictly brackish-water types; while up 

 to this time we know of no Tertiary of exclusively marine origin in all 

 this internal region of the continent. I was also, in part, influenced in 



