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Show 198 sic, Cretaceous, and even remnants of the Lignitic group, which, by the i yielding nature of the materials composing these rocks, have given l rather a smooth, rouuded outline to the surface over an extended area, i 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 Rivers, above their junction. Nearly all the sections described in this paper represent portions of the surface included within this space. Withiu this area also is inclosed one of the most complicated and instructive of the great mountain auticlinals. 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, j Plate III represents portions of a continuous section, the left- hand end i of No. 2 joining on to the right- hand eud of the upper section of No. 1, the whole forming the high wall- like range on the east side of the Gallatin'Valley, extending from a point below Flathead Pass to the I Bridger Canon to the northward. There is then a short distance in | which no rocks older than the Liguitic group are exposed. The older groups, however, re appear on the divide between the Gallatin and Yel- j lowstone Valley, crossing the Yellowstone and thus form the Lower j Canon. I In Plate VII, lower section, Second Valley of the Yellowstone, looking 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 River has cut its channel through this high ridge of lime- i stone at right angles. We have here, then, attempted to describe briefly the east or northeast 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 Carboniferous 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. j It is probable that the corresponding opposite portion of this great | anticlinal extends along the east side of the Jefferson Valley, rising ; like a slantiug wall 2,000 feet above the plains below. It crosses the Jefferson near the entrance of the North and South Bowlder Creeks, j and through this great ridge the river has worn a vast, deep, narrow I gorge called the Caiion of the Jefferson. Here 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 Stinkingwater Creek, the high limestone ridge continues westward to the | sources of the creek, to Red Rock Creek and beyond. j It is probable that the axis of the great anticlinal lies for the most ; part between the Madison and the Jeffer& on, forming the granite belt from Sterling to Summit at the head of Alder Gulch. The granitic axis also includes a portion of the country east of the Madison. The general trend of the axis is about northwest and southeast. We may |
