GEOLOGICAL SURVEY OF THE TEERITOEIES. 21 



up to the crest on the west side, and often passing what appears to be 

 the junction of the Big Horn Range, even to the entire divide of the 

 mouiitaius. We also see, high up on the flanks of the mountains, a fall 

 series of the more recent Tertiary beds, with pinkish bands, precisely 

 similar to those in the Wind River Valley. These pass up into yellow 

 sandy marls and sandstones. I have estimated the entire thickness of 

 the Tertiary beds on the west side of the mountains at 1,200 to 1.500 

 feet. In the lignite beds and vicinity are great quantities of selenite 

 and silicified wood. All over the highest hills near the crest of the 

 mountains, 10,000 feet above the sea, are the recent Tertiary beds. A 

 large portion of the superficial Tertiary strata incline from Wahsatch 

 and Gieen River Mountains, showing that these deposits were probably 

 disturbed at the same time by the uplift of these ranges. In the dis- 

 tance are the Three Tetons, rugged peaks of erupted rocks, towering 

 high above the rest. These peaks are sharply j)ointed, piercing the 

 clouds like needles, and it is said that the trappers have never been able 

 to get near them. So far as we have yet seen, at least fifty miles of the 

 dividing crest of the mountains are covered with Tertiary rocks. 



" Jtine 7. — We passed up a ravine to-day, which runs north and south, 

 and is close to the divide which overlooks Snake River. The lignite 

 strata incline nearly northeast at an angle of 40°, and as we ascend, 

 many of the lower members of the lignite strata are exposed. We also, 

 see quite large areas covered with eruptive rocks, and also a sort of 

 basaltic conglomerate composed of large angular masses of rock cemented 

 with the melted material. Mr. Bridger informed me that these same 

 formations continue all along the Wahsatch Mountains to Bear Spring 

 and Henry's Fork, and down Snake River nearly to Blackfoot Creek. It 

 also cov^ers the valley of the Yellowstone to points below the lake. 

 There is simply a band of granite along the divide in the form of a 

 narrow belt 



" Descending the Gros Ventres to its junction with the Snake River, we 

 find the same Tertiary beds prevailing to a great extent, and sometimes 

 assuming a variety of lithological characters, at one locality a thickness 

 of 200 feet of worn pebbles and sand, the whole inclining from 20° to 

 35°. Gradually the Cretaceous rocks appear along the valley of the 

 stream. A section of these rocks would be as follows : 



3. A series of sandstone, arenaceous limestone, and laminated marls. 

 150 feet ; inclination, 20°. 



2. A series of thin indurated beds of clay, sandy marl, limestone and 

 sandstone, with six or eight seams of impure lignite, which has 

 ignited in several places, giving to the earth in contact a brick-red 

 color. 80 feet. 



1. Gray ash-colored sandy laminated marls, with layers of fine sand- 

 stone. Sandy matter predominates. 100 feet. 



"In the upper beds were quite abundant fossils, consisting of a huge 

 Inoceramus, two species of Ostrea, a large Pinna four inches long, a 

 Cardinm, and many small shells. The whole deposit indicates shoal 

 "water in a shore-deposit, and there are also fragments of wood. As we 

 descend, the Jurassic is exposed with Ostrea and Belemnites densus, and 

 there is an enormous development of the red arenaceous beds, making a 

 thickness of 1,000 to 1,200 feet or more. Near the middle of the red bed 

 is a layer of gypsum 4 feet in thickness. There are other seams or 

 layers of gypsum, each with partings of the red marl. The dip is quite 

 variable, at one place 29°, at another 15°, and again 7°. 



" The Cretaceous beds differ from those on the east side of the Wind 



