460 REPORT UNITED STATES GEOLOGICAL SURVEY. 



occasionally appear in the surface of the outlying terrace, as has already 

 "been mentioned. 



In the point south of the Elkhorn white arenaceous deposits outcrop 

 in the hill-side at an elevation of 400 or 500 feet above the stream. In 

 the steep northern face of this ridge the same beds rise gradually to the 

 east, or rather southeast, and in the broken wooded ridges that inter- 

 vene between Mount Leidy and Jackson's Basin exposures of brownish- 

 colored deposits show here and there, and which apparently underlie 

 the before-mentioned beds. The lower slopes of these hills bordering 

 the valley of the Elkhoru are buried under accumulations of water-worn 

 pebbles, which make up considerable ridges and are spread over all the 

 lower portions of the plateau between the Elkhorn and Buffalo Fork, 

 the little basin into which the former stream opens showing some line 

 examples of terracing in these deposits. These loose materials are 

 chiefly composed of quartzite bowlders and pebbles beautifully rounded 

 and polished. 



Ascending the valley of the Elkhorn, a few miles above the Snake 

 bottoms its valley closes up in a narrow gorge, in which an exposure 

 of a couple of hundred feet of strata was seen. The section shows 

 75 to 125 feet of fine arenaceous clays, banded in thin layers of light and 

 dark drab color, with rusty-buff indurated arenaceous layers and soft 

 concretionary sandstone above, and containing two thin seams of lig- 

 nite, one above and one below, the strata inclining northward at angles 

 of from 12° to 20°. The drab clays are unconformably overlaid by a 

 variable thickness of yellow gravelly earth which looks like a Post-Ter- 

 tiary deposit, and so was mentioned in a preceding page, which makes 

 up the remaining height of the bluffs. Curious funnel-like sinks were 

 noticed in the drab deposits, the origin of which is not clear ; they have 

 the appearance of having been caused by the undermining of the super- 

 incumbent layers, which gave way on all sides, curving into and filling 

 the excavations. There was no indication of the burning out of coal 

 seams, by which this effect might be produced. 



The extremely broken foot-hills on the northern declivity of Mount 

 Leidy, descending to the Elkhorn, exhibit yellowish-buff sandstones and 

 light-buff to white indurated beds, which gently rise up and form the 

 basis of the peak. The latter, as also its principal spurs, is composed 

 of light-brownish or ash-colored deposits, and toward the summit, in 

 the northwest face, appear several brownish harder ledges. The brown- 

 ish deposits, at a distance, have the appearance of homogeneous fine 

 arenaceous clays, but which, it is suspected, may prove to be identical 

 with a remarkable conglomerate deposit occurring north of Buffalo 

 Fork, hereafter to be noticed. As has before been mentioned, these 

 deposits also occur in the high ridge a few miles to the east or southeast 

 of Mount Leidy, and in the continuation of the same heights, as they 

 approach the watershed, light-buff earthy or arenaceous deposits are 

 associated with the ash-colored beds. As seen from Station XL VIII, 011 

 the north side of Buffalo Fork, the whole northern flank of this highland 

 region is brought into view, affording an opportunity of studying its 

 general topographic and geological features. The brownish ash-colored 

 deposits are persistent stratigraphic features throughout the culminat- 

 ing crests, presenting, in their style of weathering, a strikingly peculiar 

 appearance. This is well display ed in the view of Mount Leidy from, the 

 latter station. The mountain, although quite isolated, spreads over a 

 considerable space, throwing out sharp, partially, wooded, and beautifully 

 sculptured spurs, differing from anything hitherto observed in the dis- 

 trict, though it is repeated in similar and probably identical deposits in 



