jE^LE.] GEOLOGY GUNNISON EIVER, 247 



CHAPTEE IV. 



Gunnison Eiyer — Elk Mountains — Eoaring Fork. 



Leaving Taylor Park, we followed to its source one of the western 

 branches of the Gunnison, which for the greater part of its course flows 

 through gneissic rocks of the same character that we saw on the west 

 side of the Gunnison, and of which they are really the continuation. 

 The course of the stream is about northeast. Near the head of the 

 creek we found the first sedimentary beds we saw west of the Sawatch 

 range, in an outcrop of blue limestone containing Zaphrentis and 8])irifer. 

 The layer in which the fossils occur is very dark in color, and has above 

 it lighter- colored layers that are non-fossiliferous. The strike of these 

 beds is north and south, and they incline about 10° to the west. As 

 we follow them southward, the strike gradually turns toward the west- 

 ward. A few miles south of this outcrop, between the Gunnison and 

 the east branch of Taylor Eiver, I ascended a high point, which I found 

 capped with the same limestone. I named it the Triangle, from the 

 shape of this capping, which was triangular. It seemed to be the center 

 of these ridges, one running toward the west, one toward the north, and 

 the third toward the south. Its height is 12,830 feet above sea-level. 

 Beneath the limestones are quartzites, probablj^ Silurian. The northern 

 side of the hill heads a small creek that joins the east branch of Taylor's 

 Creek jnst above a deep gorge. The course of this small creek is at first 

 toward the north, and then west. It rises in an amphitheater, recalling 

 the form of Horseshoe Mountain. The dip here was toward the north- 

 west, there being a sharp turn to the west in the strike, which on the 

 ridge to the north is almost north and south. As we follow the ridge to 

 the west, however, the strike turns still more until its direction is north 

 of west. Toward the south, however, the dip is toward the southwest, 

 and on the next high point, about a mile south of the Triangle, on the 

 northern part, it is toward the northeast. Between these points, there- 

 fore, there is a fold. The more southern point was visited by Dr. End- 

 lich, and I learn from him that the summit is granitic, and that the beds 

 dip away from it in all directions. I think that the cause of this folding 

 is to be referred to eruptive agencies, the evidence of which is to be seen 

 in the dikes that we find to the westward, and which will be referred to 

 presently. Before this disturbing element was present the general dip 

 was probably to the westward. The east branch of Taylor Creek cuts 

 its way at right angles to the strike across the strata that continue west 

 from the Triangle, and flows through a narrow rocky gorge, in which I 

 made the following section from north to south : 



1. Volcanic. 



2. Limestone. 



3. Quartzite. 



4. Volcanic. 



5. Sandstone and conglomerate. 

 0. Limestone. 



The first layers are very indistinct, but. enough is seen to show that 

 the dip is toward the northeast in Nos. 2 and 3. The first layer is a 

 dark-green porphyritic rock, probably trachytic. Nos. 2 and 3 are prob- 

 ably Sihirian, and are the direct prolongation of some of the lower lay- 

 ers seen on the Triangle. We see that the dip has changed. Layer No. 

 4 is a highly siliceous rock (Ehyolite?) and is in laminaj .which incline 



