i'ealk.] DESCRIPTIVE GEOLOGY — GREEN RIVER BASIN. 525 



marks the connection with the ranges of Colorado and Eastern Wyo- 

 ming. The further discussion of this question will have to be reserved 

 for a subsequent portion of the report. 



DRAINAGE. 



The main stream by which the Green Eiver Basin is drained is the 

 stream from which it takes it name. In considering the drainage, I shall 

 take up the eastern branches of Green Eiver first, and give the general 

 geological notes obtained whde following the streams, leaving the topo- 

 graphical detads to be given in Mr. Gannett's report. 



Big Sandy. — The Big Sandy Eiver joins the Green near our south- 

 eastern corner and forms approximately the eastern line of our district. 

 On the east side, in the angle between it and Green Eiver,. the beds are 

 variegated sands and marls, generally of gray and dull reddish colors. 

 These beds form bluffs on the Green a short distance below the mouth 

 of the Big Sandy, and were referred doubtfully to the Bridger Group. 



They appear to be mainly arenaceous and argillaceous, and may repre- 

 sent the base of the Bridger Group, although the point is hard to deter- 

 mine, as the line between the Green Elver Group and the Bridger Group 

 is somewhat indefinite. Professor Cope considered them of Bridger age,* 

 and they are also so colored on the map of the fortieth parallel sur- 

 vey, f These beds extend northward and eastward, and contain frag- 

 ments of vertebrate remains. We travelled northward on the west side 

 of the Big Sandy, and the area extending westward I have colored on 

 the map as occupied by the Green Eiver Group. The exposures on the 

 east side of the Green at the mouth of Fontenelle Creek and northward in- 

 dicate this to be the surface formation. Toward the south, and especially 

 in the angle between the Green and Big Sandy, there may be remnants 

 of the Bridger beds. This region affords but few outcrops, and is mainly 

 a desert-like sage-covered plateau. Desolate and barren as it appears, 

 if it coidd be irrigated it would doubtless produce all the crops permitted 

 by the altitude, for its soil contains more numerous elements of fertility 

 than many regions of the West that have been found to be highly pro- 

 ductive. The country is not to be condemned because it has the appear- 

 ance of a desert waste, and produces only cactus and sage brush pro- 

 ducts which afford but little indication of the character of the soil. A 

 number of desert localities, Salt Lake Valley particularly, have afforded 

 proof of the fertility of what was at first considered barren land. This 

 area, extending westward to the Green from the Big Sandy, is a broad, 

 almost unbroken expanse, on which there is a considerable growth of 

 grass scattered among the sage. The area is covered also partly by 

 drift, which conceals the the strata. 



At the mouth of the Little Sandy the following section was obtained : 



Section No. 1. 

 Top. 



1. Brownish gray, rather coarse sandstone, with pebhly layers, containing"! 



fragments of ukark's teeth and Goniobasis tenera, Hail | 



2. Coarse, yellowish sandstone ^50 feet. 



3. Indurated, argillaceous shales, with fragments of broken wood and shark's 



teeth 



* Report of U. S. Geol. Survey for 1873, 1874, p. 439, 

 t Atlas max) lb Green River Basin. 



