182 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



Overlapping the latter beds is a group of more modern Tertiary strata, 

 which, in 1870, I named the Washakie group. The eastern liaiit of this 

 group is near Creston, extending to a point just west of Bitter Creek 

 Station. These beds, so far as they are exposed to the eye, are made 

 up of soft clays and sands of various shades of brown and yellow, with 

 here and there a thin layer of rather hard sandstone. In several 

 places, beds of impure lignite are exposed. Fresh-water Mollusca in 

 great quantities are found from point to point. At one locality, a stra- 

 tum two feet in thickness is made up of fragments of Uniones. Near 

 Table Kock, there is a bed of sandstone that is little else than an aggre- 

 gate of fresh-water shells of the genera TJnio^ Paludina, Melania, &c. 



So far as we at present know, this is a purely fresh- water group. We. 

 may say here, that although there is an apparent unconformity between 

 this group and the Laramie group below, when exposed on the flanks 

 of the Uinta Mountains, yet where the two groups can be found in con- 

 junction and in a horizontal position, no line of separation can be 

 found. Indeed, there is no absolute physical break from the brack 

 ish-water beds of the Upper Lignitic to the summit of the Bridger 

 group, through at least 6,000 to 8,000 feet of strata. Near Bitter Creek 

 Station there is a gradual elevation of surface, by which a portion of the 

 upper beds of the Laramie group are brought up, and from thence to a 

 point about two miles east of Salt Wells Station the Laramie beds are 

 seen, inclining east and southeast at a small angle. Near Salt Wells 

 Station the railroad passes across an anticlinal valley, in which are well- 

 defined Cretaceous beds. These continue about six or eight miles, when 

 the Laramie group appears again, with a reversed dip to the west. Soon 

 after leaving Rock Springs Station, the Green River group overlaps the 

 Laramie or Lignitic beds, with a moderate inclination to the west, and 

 continues beyond Green River. The section will convey a true idea of 

 the various changes that occur in the position of the groups of strata 

 along the line of the artesian wells. 



It is not the purpose of this article to discuss the geology of this region. 

 I only wish to convey some idea of the age of the strata through which 

 it was necessary to penetrate to reach the supply of water. The details 

 of the geology will be fally set forth in the report of Mr. Clarence King, 

 which will soon be printed. A beautiful geological map of a broad area 

 in this district has already been published by Mr. King ; a few copies 

 were distributed November 15, 1875, and a notice was printed in the 

 American Journal of Science. 



The first boring given on the diagram is located at Separation, and 

 passed entirely through rocks of the age of the Laramie group. The 

 strata incline to the west. It will be seen that at 1,103 feet the water 

 rose to within 10 feet of the surface, and yielded 2,000 gallons per hour. 

 A few notes of the beds passed through are given, but the record is im- 

 perfect. 



At Creston, no water was reached at 300 feet. Some two or three 



