126 GEOLOGICAL SUEVEY OF THE TERRITOEIES. 



prolongation of the layers noticed in the last chapter as occujTing 

 at Cinnabar Mountain. Just below these outcroppings the river 

 passes through the third caiion, the rocks of which are gneissic, upon 

 which the limestones rest. On the west side of the river there are 

 fine exposures of black micaceous gneiss, inclining southeast. On 

 the opposite side there are three streams which cut their way to the 

 river through the solid granite. About a mile east of camp I visited a 

 butte of limestone which rose above the surrounding volcanic rock like 

 a huge monument. The dip was southwest at an angle of about 50°. 

 From these layers I obtained hemipronites, spirifer, and rliynclionella. 



The following day we moved our camp to the Yellowstone and 

 pitched our tents in a beautiful grassy valley on Elk Creek, about one 

 mile from the Yellowstone River. About two miles above us the East 

 Fork of the Yellowstone joined the main river. Our camp (No. 9) was 

 334 feet lower than the previous one, (No. 8.) The descent from the 

 plateau was rather abrupt, and gave us a chance to see the structure of 

 the Eocene beds, which were here composed of coarse, yellowish-brown 

 sandstones, intercalated with basalt and trachyte. The sandstones in 

 some places are conglomerate, and all are considerably metamorphosed. 

 Some of the layers contained impressions of deciduous leaves, among 

 which Professor Lesquereux has found Platanns nobilis, Fagus antipoji, 

 and a new species described in his report. The volcanic rocks, mostly 

 basaltic, contained a large percentage of iron, and, on weathering, pre- 

 sented a rusty appearance. In some I found green jasper and chal- 

 cedony. The valley of Elk Creek below our camp presented a curious 

 appearance. The river and the small streams hive cut their way 

 deeply through the Tertiary beds, leaving table-like buttes standing 

 between each one, being cap'ped with a volcanic layer, the top of which 

 is perfectly level. They are merely the remnants of layers that once 

 extended over the entire valley. Beneath the volcanic layers the soft 

 gray and brown sandstones have yielded readily to the action of the 

 water, and the canons are deep, with perpendicular walls. 



The Tertiary beds seem to rest immediately on the gneissic rocks 

 at this point, and before their deposition there was undoubtedly 

 a great deal of erosion. The thickness of the Tertiary beds, includ- 

 ing the volcanic layers, is about 400 feet. Throughout the valley in 

 which we were camped there was an immense number of granite-bowl- 

 ders of all sizes, which were evidently washed down the valley of the 

 East Fork, for we find them strewn along that river for some distance 

 above its junction with the Yellowstone. On the east side of the 

 Yellowstone, near Hell Eoaring Creek, there are some high granite 

 mountains, and the entire surrounding country is very rugged and will 

 some day form a most interesting field of study. Our time was too 

 limited to attempt to penetrate it at all. Near the junction of the two 

 forks of the Yellowstone there has been a bridge thrown across the 

 main stream. Just at this point we find an exposure of granite. This 

 passes into micaceous gneiss, which is overlaid by sandstones, on top of 

 which there is a bed of conglomerate, made up mostly of volcanic frag- 

 ments. Crossing the river we soon find ourselves surrounded with vol- 

 canic rocks. A short distance from the river there is an isolated table- 

 like butte, rising 600 feet above the level, of the river. It is capped 

 with basalt of considerable thickness, beneath which are soft Tertiary 

 sandstones. The floor of the butte is quite level, and is strewn with 

 granite-bowlders. It is evidently only another remnant of the basaltic 

 layer I have referred to above, which once extended over an immense 

 area. As we proceed up the Yellowstone, it becomes thicker. Follow- 



