60 GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



are found in every ravine and creek. !N"o experience of my own among 

 fresh-water shells of the present day has revealed them in such marvel- 

 ous profusion as they must have existed in or near this great lake in 

 tertiary times. Intercalated in the marly layers are thiu seams of fibrous 

 calcite and selenite$ some of the seams of calcite are three inches thick. 

 Three principal features appear in the rocks as we descend the creek: 

 1. A large increase of lime ; 2. Silica in the form of black chert or flint ; 

 3. The appearance of impure lignite. There are also petrified wood, 

 masses of stems of plants aggregated together, yet the beds are all 

 purely fresh-water. The style of weathering of the upper and lower 

 miocene is well contrasted by the character of the surface. The surface 

 occupied by both formations is equally arid and barren, but that of the 

 former is very rugged, forming what is usually termed "bad lands," while 

 that of the latter is more rounded and far less rugged. At the junction 

 of Henry's Fork with Green Eiver the geological structure is very com- 

 plicated and presents one of the most interesting studies I have met 

 with on the trip. At first glance the formations seem to have been 

 thrown into utter chaos, but a careful examination shows the system of 

 formations to be more complete and consecutive than in any other por- 

 tion of the West. The ridges of upheaval extend from the Uinta Bange 

 across Green Eiver, and seem to have almost entirely escaped erosion, 

 so that they are left for our examination nearly as they were thrown up 

 by the internal forces that elevated the Uinta Mountains. 



All along the northern slope of the Uintas, from Bear Eiver to Hen- 

 ry's Fork, I have sought for the absent members of the geological 

 series, and noted the evidences of erosions which are displayed on such 

 a stupendous scale. Not only are several members of the geological 

 series swept away, but also the surface is covered with an enor- 

 mous deposit of drift. But not until we come to Green Eiver can we 

 realize the vast extent of the erosion along the northern slope of the 

 Uintas. 



About eight miles above the mouth of Henry's Fork the calcareous 

 layers gradually disappear or cap the summits of the hills, and 

 beds with a predominance of arenaceous sediments come in. Beds of 

 massive yellow and gray sandstones rise above the water level as we 

 descend, until they reach a great thickness, three hundred to five hun- 

 dred feet. About four miles before reaching the mouth of the creek 

 the valley expands out on either side. On the north side the upper 

 portion of the bluff is a massive sandstone with a reddish tinge, inclin- 

 ing at an angle of 5° to 10°, while at the base the layers seem to have 

 been £>ushed up abruptly, as if there was some degree of discordancy. 

 The same beds that dip at a small angle on the north side of the stream 

 incline 50° to 70° on the south side and extend southwest toward the foot 

 of the Uintas. Then comes an open area of about four miles, occupied by 

 rather soft beds of yellow and steel-gray indurated clays, which I have 

 regarded as of cretaceous age, although I did not discover a fossil in 

 them. On the south side of Henry's Fork, at its junction with Green 

 Eiver, is a remarkable exhibition of the ridges or hog-backs, which rise, 

 ridge by ridge, to the distant summits of the quartzite nucleus of the 

 Uintas. The formations at first sight seem to have been lifted up in 

 such a chaotic manner that I could not unravel any system for some time. 



We followed the channel of Green Eiver down among the canons, with 

 the walls on each side rising twelve hundred to fifteen hundred feet, 

 but only triassic and carboniferous rocks were seen. At last we found a 

 deep dry gorge which had been worn through the ridges, on the west 

 side of Green Eiver, at right angles, thus exposing all the beds in their 



