58 GEOLOGICAL SURVEY OF THE TERRITORIES. 



On account of its exceeding beauty and poetic surroundings, I have 

 called it Lake "Annie." The barometer makes its elevation just 11,000 

 feet. This shows that the summit of the Peak is twenty-one hun- 

 dred feet above the base at the head of this valley. We descended 

 with great difficulty a sort of ravine on the steep sides of this valley to 

 the bottoms, and followed the little stream from its source at the base 

 of the peak to its junction with the main fork in the plains. As I have 

 stated above, the strata of the peak are nearly horizontal, and for sev- 

 eral miles down the valley the sides are six hundred to eight hundred 

 feet high and nearly vertical, with the strata inclining at a very small 

 angle. The bottom of the valley is full of the evidences of huge slides. 

 Immense masses of rock seem to fall down gradually, something like 

 the movement of a glacier, a certain distance each year, until they reach 

 the channel of the stream, and the debris is swept down by the spring- 

 floods. Large semicircular notches in the sides or walls of the valley 

 show most plainly how it has been enlarged in process of time. We 

 passed on our way down the valley through a dense growth of pines 

 and aspens, over boulders and among fallen timber, for about ten miles, 

 when we passed through the gorge of Photograph Eidge, and came 

 out into the wide, grassy, open foot-hills which led to our camp in the^ 

 main valley of Henry's Fork, in the plains. 



October 4. — We started down the valley of Henry's Fork to its junc- 

 tion with Green Eiver. I have previously mentioned the ridge or divide 

 between Smith's and Henry's Forks, which carries the tertiary beds up 

 against the foot-hills of the range. From this ridge to Green Eiver the 

 valley of Henry's Fork forms a remarkable line of separation between 

 the Briclger group and the lower miocene beds. This line of separation 

 is somewhat of a surface one, yet it is so marked as to attract the atten- 

 tion of the commonest observer. The valley is quite broad, and on the 

 south side the surface of the country to the summits of the mountains 

 appear smoothed downward, in part grassed over. A close examina- 

 tion will detect some thin remnants of the Bridger group, underlaid by 

 the lower tertiary beds, which have a tendency to weather into rounded, 

 gently-sloping hills. On the north side, the arid, rugged, "bad lands" 

 are very conspicuous, and rise up somewhat abruptly like a high wall. 

 On the north side of the creek, thereis a great thickness of the indurated 

 clays which I have included in the Bridger group. All the divisions 

 that I make are somewhat arbitrary. I can find no well-defined line of 

 demarkation. There seems to be no unconformability, and the dif- 

 ferent beds pass from one to the other gradually; but to the leaden-gray, 

 sombre, indurated arenaceous clays which cover a large area east of 

 Fort Bridger and weather into such unique arckitectual forms, and con- 

 tain a large variety of vertebrate remains, I have given the provisional 

 name of the " Bridger group." These beds I shall also regard as upper 

 miocene, and the calcareous layers which underlie the Bridger group 

 are so well displayed lower down on Henry's Fork that I regard them 

 as a portion of the Green Eiver group and lower miocene. Below all 

 these beds, is an . immense thickness of sandstone and clays, which I 

 group together as eocene, extending down to the cretaceous clays. 

 Intercalated with the clays of the Bridger group are beds of rusty-brown 

 and gray sandstones, all tending to a concretionary structure, and dis- 

 integrating by exfoliation in thin concentric layers. Sometimes there 

 are beds of sandstone which form an aggregate of concretions. In the 

 whole mass, arenaceous materials predominate. As we descend, the cal- 

 careous sediments prevail, until chalky limestones and marl are greatly 

 in excess. The lower miocene beds are also of a lighter color. By the 



