VALLEY OF THE LITTLE SNAKE EIVER. 187 



glass-inclusions. Immediately under the basalt is a fine-grained grayish 

 sandstone, which effervesces freely with acids, and is made up of rounded 

 grains of colorless quartz, and of red and black jasper, with a calcareous 

 cement. Some of the black particles look like' grains of magnetic iron. 



To the north and west of Fortification Peak extends a low, rolling 

 country, covered with soft, earthy material of a prevailing red color, in 

 which no outcrops are visible. The character of the soil, however, shows 

 that it is probably made up of decomposed beds of the Vermillion Creek 

 Eocene. These beds are found exposed on the western face of the Elk- 

 head Mountains, at the bay-like indentation between Mount Weltha and 

 Navesink Peak, where they consist of coarse, red sandstones, with inter- 

 calated beds of reddish and cream-colored clays and arenaceous marls. 

 The limits of these beds are not well defined, on account of the character 

 of the surface in this region, but their connection can be traced, over the 

 broad plains to the west, which will be found represented on Map II, to 

 characteristic outcrops, in such a manner that there can be little doubt as 

 to the hori-zon to which they belong. Though they present here little dif- 

 ference of angle with the underlying Cretaceous beds, they are probably 

 unconformable, as they are seen to be to the westward, and the lowest 

 beds of the series cannot therefore be definitely determined. On the Little 

 Snake River, at the western limit of the map, they are represented by yel- 

 low, coarse, gritty sandstones containing casts of Melania. 



The country west of the Grand Encampment Mountains, just to the north 

 of the Little Snake River, is a broad, high plain formed of horizontal beds of 

 various coarse sandstones, with intercalated clay beds, of the Laramie Creta- 

 ceous, lying nearly horizontal, with a gentle slope to the westward, approxi- 

 mately the same as that of the general surface of the country. These plateau- 

 like benches are covered with detrital material, and show comparatively few 

 outcrops. The nature of the underlying beds can only be arrived at by 

 occasional exposures along the bluffs of the canon-like stream-beds M^hich 

 traverse it. The best exposures were obtained along the banks of the Little 

 Snake River. The uppermost beds observed were coarse, white sandstones, 

 forming a bluff on the south side of the river, near the point where the road 

 from the Yampa crosses the Little Snake. At this point is an exposure of 



