70 GEOLOGICAL SURVEY OF THE TERRITORIES. 



Spring Station, which extend off toward Muddy and Bear Bivers, of 

 which Hay Stack Butte forms a part, are portions of the same group ; 

 if so it is a matter of great interest to trace the results of the denuding 

 forces, which have operated so energetically all over this country in 

 geological times. It forms one of the greatest charms of the study of 

 the geology of the West to trace the connections of different groups of 

 beds across intervening spaces, where they have been removed by 

 erosion alone or by the upheaval of mountain ranges, to take up the 

 broken links in the history and unite them together. As I have before 

 stated, we gradually pass up through the second series of sandstones to 

 a third series of laminated marls, with thin layers of chalky limestone. 

 Near the middle of these marls are some layers of chalcedony, composed 

 mostly of Goniobasis, masses of which are strewed over the surface in 

 great quantities. Fragments a foot square are covered on both sides 

 with beautiful specimens of Goniobasis, while about ten feet below is an- 

 other layer of limestone filled with Unios, with a few Goniobasis. Frag- 

 ments of turtle shells are quite abundant in the marly clays. These 

 laminated marls reach a thickness of two hundred or three hundred feet, 

 and weather into very symmetrical rounded hills or buttes, contrasting 

 quite strongly with the style of form of the Bridger clays, though sim- 

 ilar in type. Their shaly character is always noticeable, and their radi- 

 ating furrows, so characteristic of indurated clays, are wanting. 



Before reaching the crossing of Green Biver, nineteen miles north of 

 our camp near the mouth of Henry's Fork, a thick bed of rusty-yellow 

 sandstone makes its appearance. This sandstone is well shown on the 

 banks of Green Biver. It caps the high bluffs along the river near the 

 station on the railroad, and assists in giving the peculiar forms to the 

 hills. On Black's Fork the disintegration of this sand bed, as it comes 

 to the surface, has produced large banks of loose sand. The surface of 

 the country along Black's Fork and up to Green Biver Station is quite 

 sandy. ISTo portion of the country over which we have traveled seems 

 to be so entirely destitute of vegetation as that between Henry's Fork 

 and the railroad, and yet the soil possesses all the elements of extreme 

 fertility. If it could be well irrigated it would produce forty bushels of 

 wheat per acre. The bottoms of the streams produce good grass, and 

 are now occupied by numerous herds of cattle. 



CHABTEB VI. 



FROM GREEN RIVER STATION, VIA BRIDGER'S PASS, TO CHEYENNE, 

 WYOaiLNG TERRITORY. 



From this point to Black Buttes, a distance of seventy miles, we fol- 

 low the valley of Bitter Creek, along the immediate line of the Union 

 Pacific Railroad. The geological features of this region are of great in- 

 terest, and, inasmuch as the detailed account of them is included in the 

 chapters on the third belt, along the road from Cheyenne to Salt Lake, I 

 shall pass over this portion with only a few general remarks, sufficient 

 to connect the geological formations of the two i)oints. 



The Green Biver group can be studied to the best advantage along 

 the valley of Green Biver, where the sides of the bluff banks rise to a 

 perpendicular height of five hundred feet or more. The " cuts" along 

 the railroad, from Bock Springs to Bryan Station, aid us very much in 

 reading the true history of the strata and securing their fossil remains. 



