walcott.] COLORADO. 209 



WESTERN BORDER OR ROCKY MOUNTAIN SUBPROVINCE. 



This subprovince includes central Colorado, central and northern 

 Wyoming, South Dakota and southern central Montana. 



COLORADO. 



The probable presence of the equivalent of the Potsdam sandstone 



of the Mississippi Valley in the Colorado range was noticed by Dr. F. 



V. Hayden in 1874. He says : 



The lowest beds of sedimentary rocks are rather coarse sandstones, and conglom- 

 erate made up of water-worn quartz pebbles, with very irregular laminse of deposi- 

 tion, the whole reminding one of the Potsdam group. * * * There is considerable 

 variety in the aggregate of beds here, which may be regarded as Silurian, and we may 

 conclude that the Potsdam group is quite well represented, and that it is possible 

 that some of the higher divisions occur. These rocks require a still more careful 

 study, yet it is an interesting fact to know of their existence in this locality. In 

 the lower sandstones I found a species of Lingula, the present season, probably a 

 Potsdam form. 1 



These observations were made along William's Canon, 2 or 3 miles 

 above Colorado Springs. Of the probable presence of the "Potsdam" 

 in the South Park, on the north slope of Mount Lincoln, and on all of 

 the surrounding high mountains he does not appear to have any doubt. 

 He says: 



Before going further I will state what I believe to be the age of all tho lime- 

 stones and quartzites which seem to cover the highest mountains, and in which 

 most of tho valuable mines are found. I think there is no doubt that they belong 

 to the Potsdam group, though I was unable to discover any fossils. Dr. Peale found 

 a few obscure forms which indicated that the group is of the same age as those next 

 to the granites in Utah, which we now know are of that age. 3 



While studying the geology from Denver to Colorado Springs, Dr. 

 A. C. Peale examined and measured a number of sections passing from 

 various horizons in the superjacent rocks to the Archean. In one, ex- 

 tending from Glen Eyrie eastward to Camp Creek, there are 40 feet of 

 coarse sandstone of a grayish white, dark green, gray and brick red 

 color. This series rests upon the granite; is beneath limestones re- 

 ferred to the Quebec group, aud is considered to represent the Potsdam 

 group. 3 



On Trout Creek, in Bergen Park, 93 feet of sandstone is referred to 

 the Potsdam. 1 In a reddish sandstone superjacent to the u Potsdam" 

 a number of fossils were found that were referred to the Quebec group. 

 As now known this fauna is of Lower Silurian (Ordovician) age, cor- 

 responding to the Calciferous zone of the New York section. Another 

 section was measured on one of the eastern tributaries of Trout Creek, 



1 Report of F. V. Hayden, U. S. Geologist. U. S. Geol. Suit, of the Terr., 7th Ann. Rep , 1874, p. 35. 

 » Op. cit., p. 41. 



'Report of A. C Peale, M. D., geologist of the South Park Division. TJ. S. Geol. Surv. of the Terr., 

 7th Ann. Rep., 1874, p. 202. 

 «Op. cit., p. 208. 



Bull. 81 14 



