GEOLOGICAL SURVEY OF THE TERRITOEIES. 81 



cold. A tribe could remain here an entire season ^ell protected, while 

 the young men could go out on either side among the mountains in 

 search of game. At one point great quantities of dry pines have been 

 ■washed down from the mountain-side as if by a sort of local flood. The 

 fires frequently run over the mountains, killing the green pines, so that 

 soon after they fall down covering the ground. Here they had accumu- 

 lated in immense piles, and the Indiaus had at some period employed 

 them in building fortifications for themselves and their animals, as pro- 

 tection from their enemies. 



The well-known Bannock trail passes by this valley. ISTear the forks 

 of the Gallatin some igneous rocks rise up from beneath the limestones 

 200 to 600 feet high. They are exposed for a mile or more, and appear to 

 be the same as those composing the dike in the Devil's Slide on the Yel- 

 lowstone. The limestones have been pushed up, as it were, so tliat they 

 incline from either side, passing down beneath the general level from 

 the igneous exposure. Several quite large streams come in on either 

 side to form the Gallatin, each cutting a deep gorge through the rocks 

 from the crest to the river-bed. The main branch rises at the foot of 

 Mount Gallatin. A dome-shaped peak, which overlooks the valleys 

 of the Yellowstone and Gallatin, is one of the finest mountains in the 

 range, and commands a most extended view in every direction. The 

 forces seem to have operated with great irregularity, breaking the lime- 

 stone-crust in every direction and producing chaos. Sometimes a great 

 thickness of the beds is found in the lower valleys in a nearly -horizontal 

 position ; again they cap the highest mountains, either inclining at a 

 greater or less angle from the sides or lifted up bodily to the summit. 

 We have thus attempted to describe in some detail the geological struc- 

 ture of this remarkable valley. No man had ever looked upon it before 

 with the eye of the geologist, and very few i^ersons had ever visited it 

 for any purpose. The topography was entirely new. In a subsequent 

 report, when we have to present a general view of the geology of the 

 ISorthwest, we hope to make the subject still clearer by means of the 

 beautiful illustrative-section taken by the artist of the expedition, Mr. 

 Holmes. 



We will now return to the Three Forks and record the few hasty 

 notes taken on our return homeward by way of Helena. It is not pos- 

 sible to do justice to the geology of this most interesting region now, 

 but at some future time we hope to return to this work again. 



I have already described briefly the geological features of the country 

 about the Three Forks. The interesting synclinal shown in the cut 

 extended toward the northwest. The stage-road to Helena passes 

 along the northwest end, so that we could see the relations of the sedi- 

 mentary beds to the underlying granites. We thus ascertained, what 

 we had previously suspected, that the entire series of beds had been 

 lifted up in such a way that they now all inclined more or less past a 

 vertical, varying from 20° to 45°. On the west side of this ridge the 

 granitic rocks rise up from beneath the Silurian beds over a broad area. 

 Many of them are much rounded from having formed the bottom of the 

 old Pliocene lake. The irregularities of the surface are now filled up 

 with these lake-deposits. Passing beyond the ridge northward toward 

 Helena, we come to the broad valley of Crow Creek, about twelve miles 

 wide, a stream which flows into the Missouri from the west. The area 

 which forms the drainage of this creek is underlaid with granitic rocks, 

 and rich placer-mines ai-e wrought in the gulches of the small branches. 

 Eadersburgh was founded on the discovery of the placer- mines, and is 

 6 G s 



