198 



sic, Cretacenus, and even remnants of the Ligoitic group, which, by the 

 yiekliug nature of the materials composing these rocks, have given 

 rather a smooth, rounded outline to the suriace over an extended area. 



This sketch will serve to convey to the reader a conception of the 

 peculiar area which may be noted on the map as included between the 

 Gallatin and Jefferson Kivers, above their junction. 



Nearly all the sections described in this paper represent portions of 

 the surface included within this space. 



Within this area also is inclosed one of the most complicated and in- 

 structive of the great mountain anticlinals. 



It is only by taking this position, which seems to be borne out by the 

 facts, that we can unravel the complicated topography of this district. 

 Plate III represents portions of a continuous section, the left-hand end 

 of No. 2 joining on to the right-hand end of the upper section of No. 1, 

 the whole forming the high wall-like range on the east side of the Gal- 

 latin Valley, extending from a point below Flathead Pass to the 

 Bridger Canon to the northward. There is then a short distance in 

 which no rocks older than the Lignitic group are exposed. The older 

 groups, however, re appear on the divide between the Gallatin and Yel- 

 lowstone Valley, crossing the Yellowstone and thus form the Lower 

 Canon. 



In Plate VII, lower section. Second Valley of the Yellowstone, look- 

 ing west from Mount Delano, at the right hand, we see the Carboniferous 

 limestones inclining at an angle of 30° to 50° to the northwest. The 

 Yellowstone Kiver has cut its channel through this high ridge of lime- 

 stone at right angles. 



We have here, then, attempted to describe briefly the east or north- 

 east portion of this great anticlinal, which, in future surveys, will be 

 extended far to the northeast, beyond the limits of our geological map. 



The structure of this first portion of the anticlinal is well shown in 

 section 7, through Flathead Pass, on page 82 of Annual Report for 1872. 



In the section, we observe that the Silurian strata, which are shown 

 on the west side of the ridge, dip past a vertical, while the Carbonifer- 

 ous limestones, which form the crest, are vertical or nearly so, while 

 the Jurassic, Cretaceous, and Lignitic beds incline at various angles to 

 the northeast toward the valley of Shield's River. 



It is probable that the corresponding opposite portion of this great 

 anticlinal extends along the east side of the Jefferson Valley, rising 

 like a slanting wall 2,000 feet above the plains below. It crosses the 

 Jefferson near the entrance of the North and South Bowlder Creeks, 

 and through this great ridge the river has worn a vast, deep, narrow 

 gorge called the Canon of the Jefferson. Hei'e the river, for a distance 

 of five miles, flows through nearly vertical walls of limestone, rising on 

 either side from 700 to 1,200 feet. The general dip is apparently toward 

 the west, or perhaps southwest. A very high ridge extends nearly north 

 and south between the Jefferson and the South Bowlder Creeks. This 

 ridge is cut through by the Stinkingwater, a branch of the JeffersOn, 

 thus forming a broad, valley-like opening, through which the road passes 

 from the Jefferson Valley to Virginia City. On the west side of Stink- 

 ingwater Creek, the high limestone ridge continues westward to the 

 sources of the creek, to Red Rock Creek and beyond. 



It is probable that the axis of the great anticlinal lies for the most 

 part between the Madison and the Jefferson, forming the granite belt 

 from Sterling to Summit at the head of Alder Gulch. The granitic axis 

 a^so includes a portion of the country east of the Madison. The gen- 

 eral trend of the axis is about northwest and southeast. We may 



