ENDLicH] SOUTHERN AREA MUD SPRINGS. 129 



posed of the latter, producing a very brilliant effect of reflection in the 

 sunlight. East of Creston we are once more fairly in the Laramie Group. 

 Isolated beds of the former occupy some of the higher points east of the 

 border of the Wasatch ; but the upper members of the Laramie and the 

 lower ones of the Wasatch are so very much alike that it is almost an 

 impossibility to separate them. Within the region where we had occa- 

 sion to observe these two groups in contact, I noticed no evidence oi 

 any unconformability. Indeed, it was often only by the aid of the higher, 

 colored beds that I was enabled to draw the dividing line. 



So far as could be determined, the Wasatch beds reach northward 

 very nearly to the granites between Sweetwater and Whiskey Gaps. 

 From there westward their limits are determined first by the Sweetwater 

 Group and then by the Green Elver series. On the east side the termi- 

 nation of the Wasatch is characterized by the appearance of the Laramie. 



Section XVI* illustrates the relative positions of the groups above dis- 

 cussed. The older strata, which make their appearance farther south. 

 are represented as taking part in the anticlinal upheaval (D), which 

 terminates directly north of Salt Wells. Colorado shales (e) are the old- 

 est beds exposed on the surface. Dipping off in either direction we find 

 the Fox Hdls series (/). This is overlaid by Laramie (</). Both the 

 upper (n) and the lower (o) horizons in which coal is found have been 

 marked. 



Covering the Laramie, after a short area of out-crop to the west, a 

 longer one to the east, we find the Wasatch Group (h). Eastward this 

 forms a shallow synclinal basin. This, taken in connection with the 

 general dip to the southward, produces the Shoshone Basin. Green 

 River beds (i) overlie the Wasatch to the westward, but farther east are 

 found only in scattered remnants along this line. Basaltic eruptions (k) 

 have been represented. They occur quite frequently in the Wasatch. 

 Two extensive drift-areas (I and m) are found in the Shosbone Basin 

 and on Packer's Creek, the latter being west of the anticlinal. 



Some very interesting information may be obtained regarding the dis- 

 tribution of these groups from the section of artesian wells bored along 

 the Union Pacific Railroad.t The greatest depth reached by boring 

 along this portion of the road is at Eock Springs, 1,154 feet. This pene- 

 trates the entire Laramie Group and reaches down far into the Fox Hill 

 series. From the data here obtained, the position of the Wasatch ap- 

 pears to be constant, and the distribution of coal, in two horizons, to 

 remain equally so. 



Mud springs. 



It has been mentioned above that near one of the lakes in the Sho- 

 shone Basin a large number of mud springs were found. They have 

 been partially described in the itinerary. On the eastern shore of Death 

 Lake we observed mounds shaped like bee-hives, which generally con- 

 tained a circular opening near the top filled with muddy water. They 

 are located about 50 feet above the lake surface, but extend downward. 

 to the water's edge. Within the region there is no flowing surface-water. 

 We found that the mounds varied from a few inches in height to about 

 1 5 feet. None were found containing water higher than 4 feet. They 

 are circular or oval upon cross-section, and the opening containing the 

 water adapts itself to the shape of the mound. A mound of 4 feet in 



* I may here state that none of the sections are prepared on scale, owing to the want 

 of a reliable map. — E. 



t Bulletin U. S. Geol. Surv., vol. Hi., No. 1, Dr. Hayden "On Artesian Borings," &c, 

 p. 1-1. 



9 a s 



