56 CARHONIKEKons FORMATIONS AND FAUNAS OF COLORADO. 



Ill the Aspen district tin- Miiroon t'oriiiiition jj-riuiuates into a bright-red 

 sandstone wliieli Sjmrr refers to the Triassic. In the Tenmile district the Maroon 

 forination is siieeoeded by a series of sandstones of an intensol}' brick-red color. 

 These are correlated upon the evidence of their lithoiogic position with the W\'ouung 

 sandstone of the Front Range, the name being derived from the Denver Basin area. 

 All the evidence except that of a paleontologic nature, since fossils have been found 

 in neither formation, indicates that the Wj'oming formation of the Tenmile district 

 corresponds to the Triassic of Spurr's section at Aspen. The latter has a thickness 

 of 2,600 feet in Lenado Canyon, while the Wyoming formation is but 1,500 feet 

 thick: l)ut as the Wyoming is immediately succeeded in the Tenmile area by 

 Quaternary deposits, it is possible that it may have suffered erosion, and that this 

 measurement does not indicate its original thickness. At Aspen the "Triassic" is 

 overlain b}- the Gunnison formation, with an unconformit}^ between, so that its 

 thickness there also is probablv not the original thickness. 



Spurr, as we have just seen, places this formation in the- Trias, but Emmons 

 groups it with the Carboniferous formations, remarking that "If the Permian is 

 represented in Colorado, the evidence of which appears to the writer as yet very 

 uncertain, it would be included in these beds, which have evidently been deposited 

 in direct and unbroken succession over the Upper Cai'bonif erous. " From facts 

 which I will discuss later, it seems to me rather more jsrobable that the W3'oming 

 formation is in fact of Triassic age. 



Aside from the two monographic works brietlj^ discussed, but little has been 

 written upon the Grand River region that calls for remark, although considerable 

 literature of an occasional character centers about the mining camps of Aspen, Red 

 Cliff, etc. 



Possibl}' before being diverted to the consideration of some of the earlier litera- 

 ture, it would be well to speak here of the geologic section at Red Cliff', which has 

 been briefly described by Emmons (in 1886)" and by Tilden the year following.* 

 Emmons speaks of the series as being practicalh' the same as at Leadville. The 

 Blue or Leadville limestone and the Cambrian quartzite are the same in both areas and 

 have the same thickness. The total thickness to the top of the Leadville limestone 

 averages less than 500 feet at Red Cliff, as against 600 feet at Leadville. This is 

 owing chieffy to the White or Yule limestone, while the Parting quartzite was not 

 definitely recognized, though thin siliceous beds occur at about the horizon for it. 



Tilden's section, which was made at Battle Mountain, near Red Cliff', in Eagle 

 County, is more detailed and runs as follows: 



aColorado Sci. Soc, Proc, vol. 2, pt. 2, pp. 85-105. 



6 Colorado State School of Mines, Bienn. Kept, for 1886, 18S7, pp. 129-133. 



