GEOLOGICAL SURVEY OF THE TEERITORIES. 77 



by tlie water aud cemented into a breccia. Deep into these ridges the 

 little streams have cut their channels in past ages, forming what should 

 be called valleys, rather than cailons, with almost vertical sides, Avith 

 rocks cropping out here and there, covered mostly with grass or trees. 

 These ravines, 500 to 800 feet deep, occur one after the other in great 

 numbers, many of them entirely dry at present, but attesting the pre- 

 sence and power of aqueous forces at no very remote period in the 

 past, compared with which those of the present are utterly insignificant. 



Not until surface geology receives greater attention than it has done 

 vL]) to this time will we comprehend the vastness of the agencies which have 

 wrought out the wonderful results which we see everywhere around us. 

 What were the forces that wrenched from the parent bed masses of gran- 

 ite, from one ton to five hundred tons weight, rounded off the angles and 

 lodged them upon the plains 300 to 500 feet above the channels of the 

 principl astreams'? Along the East Fork, for twenty miles above its 

 mouth, on the west side, there is a sort of terrace about a mile in width, lit- 

 erally covered with the granite bowlders which have been swept down tbe 

 valley from a short distance above. The granitic rocks, of various textures 

 and composition, are here exposed in full force. Hell-Koaring Mountain, 

 at the entrance of the creek of that name, is a huge peak composed of 

 stratified gneiss. Some of the strata, however, are 50 to 100 feet in 

 thickness, massive red or gray feldspathic granite. Just opposite the 

 entrance of the stream there is a splendid exhibition of black micaceous 

 gneiss, inclining 14^' southeast. It seems to form a vertical wall on the 

 right side of a little creek that flows into the Yellowstone from the west, 

 while on the left side the entire mass of the hills, for miles in extent, is 

 composed of the usual variety of igneous rocks. These incline in the 

 opposite direction, northwest, 10^ to 150; so that this small stream, now 

 not more than 4 feet wide and 6 inches in depth, has, at some period, had 

 sufficient x)0wer to cut its channel two hundred to four hundred yards 

 wide, through the hardest rocks, 500 to 1,000 feet in depth, to the level 

 of the Yellowstone, into which it flows. Hell-Eoaring River is quite a 

 large stream, rising high in the dividing range to the east, and flow- 

 ing with tremendous impetuosity down the deei) gorges, thus receivmg 

 its peculiar name. The mountains on either side are among the 

 most rugged in the Yellov/stone country, and seem to defy access. They 

 come close down to the channel of the Yellowstone on the east side, 

 so that traveling on that side is attended with great difijculty. On the 

 west side the broad, high, irregular, step-like terrace, or rather group 

 of foot-hills, 300 to 800 feet above the bed of the Yellowstone, is quite 

 easily traversed, and a road for wagons could be made without much 

 labor. There are some steep hills which, at the present time, appear 

 formidable, but a careful exx)loration might bring to light a route that 

 would avoid them mostly. 



After crossing the high divide, between the drainage of Gardiner's 

 Eiver and the group of little streams that flow into the Yellowstone on 

 the west side, of which Tower Creek is the most conspicuous, we come 

 to the region of wonderful ravines and canons. Layers of basalt have 

 been i)oured out over the basis rocks, of whatever age they may be, at 

 different periods ; at the same time vast quantities of fragments of basalt 

 were cemented together with a fine volcanic dust. In the process of 

 wearing out the ravines and caiions on either side, hundreds of curious 

 pinnacles and columns, resembling groups of Gothic spires, were carved 

 out of the solid beds of basalt and breccia. On the east side of the Yellow- 

 stone, the sides of the mountain rise step-like, and, at different eleva- 

 tions, the basalt has poured out and overflowed like the de])osits of 

 hot springs, except that the deposit is a dingy-black color. These out- 



