242 GEOLOGICAL SUKVEY OF THE TEREITOEIES. 



tends very far to tlie north of Grizzly Peak. On Massive Mountain the 

 rocks are mainly gneissic, with alternations of a i^orphyritic granite, or 

 rather granitic porphyry, with seams in places of quartzite and a horn- 

 blendic volcanic rock. The general dip seems to be toward the north- 

 east. To the southwest of the peak the dip seems to be toward the north 

 and northwest. At the head of Roaring Fork, opposite the head of the 

 Gunnison, the dip is to the northwest, and the angle of inclination about 

 50°. Between the two there is a continuation of the eruptive rock of Griz- 

 zly Peak, but to what extent I am unable to say. The gneiss is mostly 

 dark and micaceous, with alternating beds of coarse white granite, in 

 layers from four to eight feet in thickness. The country all about is very 

 rough and rugge'd, making traveling very difficult. 



Between the head of the Arkansas and the head of Eagle Eiver there 

 is a low pass — Tennessee Pass — the elevation of which is 10,242 feet. 

 The upper part of the river flows through granitic rocks, in which there 

 are occasional dikes of volcanic rock. The river flows through a canon 

 for about three miles, when it emerges into a broad, oi)en valley about 

 four miles in length and three wide. Here the sedimentary beds again 

 make their appearance, dipping a little north of east at an angle of 5° to 

 10° Eesting on the gneiss there ai"e quartzites about 200 feet in thick- 

 ness, above which there are limestones, succeeded by shales and brown- 

 ish sandstones. Mr. Holmes obtained some fossils here — Spirifer, Pro- 

 ductus, Grinoids, &c. On the western side of the creek we have the lower 

 quartzites capping the granites — the continuation of the same beds on 

 the eastern side of the valley. At the head of the valley a large branch 

 comes in from the east. Toward the head of this creek there seems to 

 be a slight change in the dip. The beds which before were horizontal, 

 or nearly so, 'and having a dip on the main stream to the eastward or 

 northeast, now are slightly inclined to the westward, influenced- proba- 

 bly by the Blue Eiver range. On the west edge of that range I am in- 

 clined to think there is a fault, the continuation of one of the faults west 

 of Mount Lincoln. I hope to be able to study this region more closely 

 next season, so that it may be determined. 



Just below the meadow, the creek enters a caSon, and the line of the 

 sedimentary beds crosses the creek. The trail here leaves the branch 

 coming from Tennessee Pass, and crosses to a large branch coming from 

 the west. Por about four miles of its course, it is parallel to the other 

 stream, and on the low ridge between them capping the schists there is 

 a layer of quartzite, and on the east side of the cafion of the main 

 branch we have all the layers from the Silurian upward at least to the 

 Upper Carboniferous. At' the mouth of the Western Fork, a high hill 

 stands between it and the other fork, capped with the Silurian quartz- 

 ites. Here the main river enters a deep and rough inaccessible caiion. 

 The trail keeps high up on the hills overlooking it. Sedimentary beds 

 are shown on both sides. On the west are only the quartzites which I 

 have referred to — the Potsdam group. On the eastern side, however, 

 we have beds at least as far as the Permian, and if we could have gone 

 far enough to the eastward I am satisfied I would have found the Triassic 

 sandstones on top, and perhaps even the Jurassic layers. Mr. Holmes 

 says that farther north, on Eagle Eiver, not only is the Jurassic present, 

 but also the Cretaceous. This was west of Mr. Marvine's district, and 

 will be the subject of future investigation. The creek rising just north 

 and west of the Holy Cross Mountain, and flowing to the northeast into 

 Eagle Eiver, was once the seat of intense glacial action, and the valley 

 now presents us with the most beautiful example of what is on the Alps 



