256 GEOLOGICAL SURVEY OF THE TERRITORIES. 



the beds that were turned over beyond the vertical have resumed their 

 original position, and the ends have been draggled in, as shown in Fig. 

 ], Plate XVIII, which represents a section made west of White Eock. 

 The peak is made up of eruptive granite, and is 13,671 feet high. Kear 

 the base I found micaceous hematite coating the surfaces of the granite 

 debris in radiating crystals. The rock near the summit is very much 

 broken up, rendering the ascent of the peak a little dangerous in places. 

 North of the peak the summits of the ridges are capped with sediment- 

 ary beds, dipping north and northeast. All the mountains in this mass 

 have conspicuous amphitheaters, in which there are snow-banks and 

 small lakes, the latter generally frozen. Eeturning to the mouth of 

 Teocalli Creek, we find ourselves in the broad valley of East Eiver. 

 East Eiver flows through Cretaceous rocks. Below the mouth of Slate 

 Eiver, the largest western branch, are several beautiful terraces. The 

 Cretaceous area extends southward into Dr. Endlich's district. Below 

 the mouth of Slate Eiver, on the west side of East Eiver, beyond the 

 valley, the Cretaceous rocks are covered by an overflow of trachyte. 

 As we come around from Teocalli Creek to East Eiver, the most strik- 

 ing points are " Crested Butte " and "Gothic Butte," which stand be- 

 tween East Eiver and Slate Eiver. Tliey are both isolated, and rise 

 considerably higher than the surrounding country. Both are sur- 

 rounded with cretaceous shales. Crested Butte is the more southern of 

 the two, and is 11,838 feet in height. It is composed of eruptive gran- 

 ite, similar to that on Italian Mountain and White Eock. Between the 

 two buttes there is an exposure of trachyte, which is probably continu- 

 ous with a band that is seen in Gothic Butte. The latter is six miles 

 from Crested Butte. It was visited by Doctor Hay den, and to his report the 

 reader is referred for the details of its structure. The summit is trachytic. 

 Whether this is only a capping or not I cannot say positively. I am 

 inclined to think, however, that it is not merely a capping, but that its 

 relation to the surrounding beds is as shown in Fig. 1, Plate XVII, at a. 

 Below the trachyte that is seen on the summit are cretaceous shales on 

 the side of the butte, and below a second layer of trachyte. On the oppo- 

 site side of the valley Mr. Holmes found in the shales of Xo. 2 Creta- 

 ceous, a bed of trachytic rock. This extends for some miles. I think 

 that this mass is intrusive, and is connected with the trachyte of the 

 butte. Mr. Holmes was unable to determine the line of junction 

 between it and the beds above. I but little doubt that the shales just 

 above will be found changed to a greater or less degree near the tra- 

 chyte. I have before referred to the inversion of the beds on the north- 

 east side of Bast Eiver. These inverted beds are seen in Fig. — , Plate 

 XVII, the Silurian being on top. The lower beds are all cretaceous. 

 At the head of a small branch of East Eiver we have bluffs of these 

 beds dipping to the northeast about north 55^ east, at an angle of 20° 

 to 25°. First are about 100 feet of very thinly laminated black shales, 

 nou-fossiliferous. Xext are yellowish sandstones and shales for about 

 150 or 200 feet. In the lower part of these shales fragments of stems 

 and leaves are found. I saw also some poor specimens of inoceramus. 

 Above we have black shales. How far they extend I was unable to 

 determine, the slope being grassed over. On another small creek, the 

 one seen to the right of a hill, the first exposure is a bed of white hme- 

 stone shown at /, Plate XVII. Below, or rather above, as the beds 

 are inverted at the point e, Mr. Holmes found fossils of Xo. 3 Creta- 

 ceous. This bed of limestone is, therefore, probably the same white 

 bed that is seen in the Cretaceous all along the foot-hills on the edge of 

 the plains. It is bed Xo. 1 in section Xo. 1, and Xo. 44 in section Xo. 



