120 GEOLOGICAL SURVEY OF THE TERRITORIES. 



breccia. The prevailing color of tins breccia is a gray, but the included 

 masses have an almost infinite variety of color, green, purple, and red 

 masses being abundant. 



On the -!4th of July, in company with Messrs. Wakefield and Savage 

 of the expedition, I started up Caiion Creek from cam]) No. 5 with the 

 intention of crossing the hills west of the second canon and striking 

 the Yellowstone Eiver near Cinnabar Mountain, where the party ex- 

 pected to camp. The valley of Caiion Creek is quite wide and well 

 watered, there being several small lakes bordering it. We followed the 

 course of the stream but a short distance, when we struck up on the 

 hills. The volcanic rocks here seem to be in contact with the gneisses. 

 Scattered among the volcanic rocks I found silicified wood in abundance. 

 Alter a long and arduous climb over the lower hills we reached a long 

 ridge of volcanic breccia, which seemed to be at-purof the main ridge, 

 and to the suininit of which it led. It projected from it at a right angle. 

 So following it up we at last gained the top, and found ourselves on the 

 edge of a precipice, which formed a portion of the opposite side of the 

 ridge. Looking over the precipice we saw we were on the top of a 

 blank vertical wall of over 2,000 feet in height. The elevation of the 

 mountain we were on was 9,478 feet above sea-level and 4,.377 feet above 

 the camp (No. 5) we had just left. The view from the summit, how- 

 ever, repaid us well for our toilsome climb. To the south and west the 

 entire country seemed to have been subjected to the most intense vol- 

 canic action, followed by an immense amount of erosion. Somber- 

 colored ridges, with sharp, piercing peaks and conical crater-like points, 

 with deep gorges between, testify to the former disturbances. All about 

 US were deep banks of snow. In order to descend we were obliged to 

 follow the ridge toward the north until we came to a spur projecting at 

 right angles from it. This spur sloped gradually to the valley of Cin- 

 nabar Creek, a small stream tributary to the Yellowstone River. We 

 descended on this spur to Cinnabar Creek, and then followed it around 

 Cinnabar Mountain, reaching camp at night-i'all. Cinnabar Mountain 

 shows a patch of the sedimentary rocks that everywhere else near here 

 seemed either to have been covered by the outflow of lava or to have 

 been washed away. It is probable that both causes have operated. 

 The northern portion of the mountain is made up of granitic rocks, a 

 continuation of those seen in the second caiion. Upon these rocks rest 

 quartzites, followed by limestones, the ui)per layers of which are un- 

 doubtedly Carboniferous. The liluestoues are followed by quartzites 

 again. One ridge of this quartzite forms the northern wall of the 

 Devil's Slide, while the southern wall is formed of a dike of dark-greeu 

 I porphyritic rock. This dike probablj^ separates the Carboniferous from 

 The Jurassic. Between these two almost vertical walls the softer ma- 

 i terial has been washed out. Adhering to the dike are pieces of a blue-clay 

 slate, and following it we find Jurassic beds of slates and limestones con- 

 : tuimug Myascitessubcom2rressa, Fholadomya., and Camptonectes. Nextcome 

 Cretaceous beds, in which there are indications of coal, and containing 

 Scophitcs, Vcntricosa, Bacnlites^ Ostrea, Inoeeramtis, and Trigonia. All the 

 beds I have mentioned above have a dip to the southwest and an incli- 

 tion of from 50° to 80<^. About a half mile above the Devil's Slide we 

 find that the beds seem very much crushed together, and within a very 

 short dista7ice dip southwest, and are horizontal and dipping northeast. 

 A visit to one of the high peaks in the neighborhood gave us a clew to 

 this curious contortion of the strata. 



On the morning of the 26th of July Messrs. Gannett, Brown, and 

 myself started to make the ascent of the peak, which lay to the south- 



*: 



