56 GEOLOGIC VL SURVEY OF THE TERRITORIES. 



the Madison, through which the river has carved the Middle Canon. The 

 modern deposits in this basin are quite extensive, reaching an aggre- 

 gate thickness of 400 to 800 feet, but they are composed mostly of vol- 

 cani(5 sand and gravel or coarse drift-material, much worn, with only a 

 small proportion of the light-gray marls, which we find so abundant in 

 the valley of the Three Forks. Vast quantities of rounded bowlders 

 are scattered over the surface, all of which, so far as I could ascertain, 

 are of volcanic origin. This basin is mostly covered with a thick growth 

 of i)ines, with here and there open meadow-like spaces or parks. 



From this basin we made a short side-trip to Henry's Lake, which 

 forms the source of one of the main branches of Snake River. After 

 traveling several miles across the bottoms through dense pine-woods, 

 we came out near a good-sized stream, which flows into the Madison 

 from the west. Crossing this we have a broad open meadow for several 

 miles until we reach the Tahgee Pass, which leads over to the valley of 

 Henry's Fork. The scenery was very attractive in every direction. 

 This branch, which has never yet been laid down on any of our maps, 

 is about 100 feet wide, and on an average one foot deep, and winds 

 most sinuously through the low, boggy bottom. We followed the old 

 Tahgee trail to the East or Tahgee Pa ^s, named years ago after the head- 

 chief of the Bannacks. This is a low level pass over which a coach and 

 four might travel on a gallop. It is underlaid mostly with limestones, 

 but as we approach Henry's Lake, the quartzite and gneissic rocks 

 appear beneath the limestones. The lower portion of these unchanged 

 rocks are pebbly arenaceous limestones and sandstones. The pebbles 

 are much worn, and are either quartz or micaceous gneiss, showing that 

 the sediments were derived directly from the metamorphic rocks. 



In this pass there is a group of huge hemlocks that will at once arrest 

 the traveler's attention. They seem to belong to another age. There 

 are ten of them, and several others have perished. They are four to 

 six feet in diameter, and rise to a height of 100 to 350 feet. This group 

 of trees is the more conspicuous from the fact that they are larger than 

 any others in this region, and have a very ancient appearance. 



There is one peculiarity of the tree- vegetation all over this portion of 

 the West, that it has a fresh, young look. The pines are seldom more 

 than two feet in diameter, sending up a straight stem 100 to 150 feet 

 high, and a large aged pine, or tree of any kind, is a landmark as well 

 as a curiosity. We ascended the mountains on the north side of Henry's 

 Lake, and from this point obtained a fine view of the country in every 

 direction. The view down Henry's Fork was remarkably flue. The air 

 was clear and pure, and the valley to the junction with Snake Piver was 

 spread out like a picture, while the magnificent range of the Tetons, full 

 fifty miles distant, seemed not half that distance. The metamorphic rocks 

 are best shown on the west side of this range. Henry's Lake was at 

 our feet, shallow and full of little islands, only a remnant of its former 

 self. To the west there is a beautiful grassy valley, with a small stream 

 that flows into Henrj's Lake. This valley leads up to the divide from 

 which the west fork of the Madison takes its rise. South of this val- 

 ley there is a belt of metamori)hic rocks extending off far to the west, 

 rising 800 to 1,200 feet above the lake. On the south side, and extend- 

 ing to the southwest toward Ped Pock Lake, is another valley, which 

 forms a beautiful pass. The low belt of mountains between these two 

 passes is grassed over or thinly-wooded with pines. While the range 

 on the south side of the lake, which extends ofi'in a southwest direction 

 from Henry's Fork Valley, is very heavily timbered. This is a tine 

 range, and is at this time covered with large patches of snow. The 



