PEALE.] 



GEOLOGY ELK MOUNTAINS, 259 



The dip is north 55° east. At the point a in the illustration (Fig. 2, 

 Plate XYIII) the angle of inclination is 58^, and at h it is 35o. Bed 

 'No. 10, in section No. 27, is the sandstone of "isTo. 1 Cretaceous," and in it 

 Mr. Holmes found some fragments of leaves, none, however, very dis- 

 tinct, but sufficient with the lithological characters to identify the bed. 

 The layers just above should probably be referred to the Jurassic. Fig. 2, 

 Plate XVIII, represents a section through the Elk Mountains, near 

 the head of Eock Creek. Section No. 27 was made from a to c. 

 Whether the line of junction is exactly as represented at d in the 

 illustration cannot be definitely determined until the line shall have been 

 followed throughout its entire extent. The granite probably makes its 

 appearance in places along this line. On the eastern branch of Eock Creek, 

 (e in the figure,) which is in part of its course parallel to the main stream, 

 the Carboniferous or Permo-carboniferous rocksare exposed at thebottom 

 of the valley, and above them forming high blufi'-like walls. On either 

 side are red sandstones dipping north of east. Near its head the main 

 branch of Eock Creek turns to the west, and at this point the dip of 

 the rocks also changes. On the north and west side of the creek, in the 

 space formed by this turn, is Treasury Mountain, so named from the 

 discovery there of lodes of silver-bearing galena. At the sooth end of 

 the mountain the dip of the sedimentary beds is south 5° east, and the 

 angle of inclination is about 12°. As we follow the course of the creek 

 the dip changes as the creek turns, and on the west side it is east of 

 north. Treasury Mountain is composed mainly of cretaceous shales. 

 Toward the west there are gypsiferous beds. At the point where the 

 mines are situated, black shales containing quantities of Inocerami pre- 

 vail. They are all very much changed, probably by the intrusion of the 

 metaliferous lodes. The latter are described in Dr. Endlich's report.* 

 On the east side of the creek, opposite Treasury Mountain, there 

 seems to be either a bend or a fault in the Cretaceous beds ; the 

 shales at one place appear to dip toward the northwest. I did not 

 have time to investigate it, but I am inclined to regard it as merely 

 local. As we go down the creek the beds on the right sicle still occupy 

 an inverted position. Just below the mouth of the eastern branch of 

 Eock Creek, it enters a deep caQon. Here, below the cretaceous rocks, 

 the older formations, at least as far as the Carboniferous, are exposed, 

 as shown at a in Fig. 3, Plate XVIII. Following the eastern branch wo 

 cross the No. 1 Cretaceous twice. The second time the bed is inverted, 

 as abo"ve it we find the older beds, which are beautifully shown on both 

 sides of the deep gorge-like valley, dipping toward the northeast at an 

 angle of from 50° to 60°. There is, therefore, probably a fold as indi- 

 cated in the illustration. In the cretaceous rocks at & a dike outcrops. 

 The creek, as it flows over the edges of the cretaceous rocks, does so in 

 a series of beautiful cascades and falls. As we continue up creek the 

 beds become more and more horizontal, until they dip slightly in the op- 

 posite direction, and we have a synclinal fold, the center of which is 

 filled with Silurian beds, for the layers are still inverted. The ends of 

 these beds, c, seem to have been broken away from those which outcrop 

 in the caGon at a. We next cross a comparatively narrow belt of gran- 



* Mr. E. A. Kirker, "who is interested in tie mines here, showed me specimens of coal 

 found in this region. He did not disclose the locality, and I did not discover it. From 

 his description of it, however, I judge it occurs in the Cretaceous rocks that prevail 

 about the heads of Slate Eiver, Washington Gulch, and East River. In appearance 

 these specimens approach anthracite more closely than any other coal I have seen in 

 the West ; how closely, an analysis will have ]to prove. It has a luster like anthracite, 

 and is very hard. I think, however, that it is only an altered Cretaceous coal. I 

 judge it to be of excellent quality. 



