HATDEX.J GEOLOGY FEOM ELK MOUNTAINS TO MIDDLE PARK. 77 



jnst on the verge of the horizon, is a high range called the Elk Head 

 Mountains. Long, high ridges rising to the limit of perpetual snow may 

 be seen far to the west, apparently composed of stratified rocks. 

 Through these ridges the little streams have cut deep gorges as they 

 flow westward to the Colorado Eiver. These gorges must i>resent most 

 excellent sections of strata to the geologist. 



Here and there we can see the whitish marls and sands of the modern 

 lake-deposits on the upturned edges of the variegated beds. In tbe deep 

 basin of the Middle Park these Pliocene or Post-pliocene deposits are 

 quite conspicuous. Tbe rocks which compose the great mass of the Blue 

 range may be called granites. Much of tbe rock is banded and strati- 

 fied, but the older portions are massive and solid, that is, the lines of 

 bedding are wanting. 



From Mount Powell we descended the west side of the mountain 

 again, and returned to Eagle Eiver. The evidence of the former ex- 

 istence of a large glacier extending up into the mountains in various 

 directions and filling up the valley of tbe little stream is quite clear. 

 The valley is oval in shape, and about four miles from the base of the 

 mountain closes up into a narrow channel, in which are a number of 

 morainal ridges. Above the ridges is a small lake one-fourth of a mile 

 wide, which was undoubtedly formed by the glacier. The high ridges 

 on both sides are covered thickly with rounded bowlders. Interstrati- 

 fied with the red sandstones are some thin layers of limestone, in which 

 are numerous fossils, Crinoids, Corals, Productus, &c., with other forms 

 which are unmistakably of Carboniferous age. 



The dip is very slight, hardly more than 3° for several miles. The 

 fallen timber is a great obstruction to traveling. In the autumn the sur- 

 face becomes as dry as tinder, and the fires run over the country, 

 destroying the life of the pines as they stand. The winter and spring 

 winds prostrate them in every direction, so that they sometimes form 

 a net- work 5 or 6 feet high for many miles. 



As we descend Eagle River below the mouth of Eoches Moutonn^s 

 Creek, the valley closes up for several miles, but expands out again to 

 half a mile in width, with soft beds on both sides. High on the mount- 

 ain-slopes are thick groves of poplar or quaking asp. A group of beds 

 comes in on this stream about ten miles below the Eoches Moutonn6s 

 Creek, 1,200 to 1,500 feet in thickness, which appears to be separate from 

 the regular formations, apparently a partially fresh- water deposit, for in 

 some thin layers of impure limestone were numerous small shells like 

 Planorbis, and Physa, and the lower 400 feet are composed of very thinly 

 laminated shales, while the upper portions are very gypsiferous, and 

 might be called gypsiferous clays and marls. 



This group appears A^ery abruptly, and continues down the river for a 

 few miles, and then disappears as if it formed a sort of basin in the va- 

 riegated groux). Whatever may have been the origin of this curious gyp- 

 siferous group, it seems to be local, and to lie in the Carboniferous or 

 between the Carboniferous and the Triassic. 



We traveled along the valley so rapidly that I could only examine 

 the immediate channel of the river ; and I here present these hasty 

 observations to call attention to tbe group. The whole district will be 

 studied in detail during the summer of 1874. 



Above the gypsiferous group is a series of the brick-red beds, 500 feet 

 or more, and still above a series of variegated beds 400 to 500 feet tbick. 

 In the lower portion of the gypsiferous group, in a bed of limestone, 

 I found a species of Productus and a Spirifer, all Carboniferous forms. 



Above the gypsiferous group, and just below tbe brick-red beds, I 



