RESUME OV LITERATURE. 65 



river." So far but about 3,600 feet have been correlated with the Maroon formation, 

 which at Aspen has a thickness of 4,000 feet, as the equivalent series has in the 

 Tenmile district. It is quite clear to me that strata are included in the Permian 

 of the lower Eagle River section that are higher than the highest of the Permian of 

 the upper section, but just how great a thickness, if any, is equivalent, and whether 

 the supei'jacent portion belongs to the Maroon formation or to the Red Beds, are 

 questions difficult to answer. I shall return to this point presentlj'. 



Peale's Dakota group seems to correspond to that to which Spurr applied the 

 same name at Aspen. His Jurassic is marked by characters similar to those of the 

 Gunnison formation of that region, and I think that they will be found to be equiva- 

 lent. If, as seems probable, the unconformity which preceded the Gunnison in the 

 Crested Butte and Aspen regions was present where Peale obtained his section, it 

 appears to have escaped his notice. Peale's Triassic is the well-known Red Beds 

 series, and can probably be correlated in a general way with the Triassic of the Aspen 

 and with the Wyoming sandstone of the Tenmile district, but the former has a thick- 

 ness of 2,600 feet, and the latter of 1,500 feet, while Peale's Triassic, which is repre- 

 sented only in the lower Eagle River section, measures less than 1,000 feet. If, 

 however, to this series be added the upper portion of that which underlies it, called 

 Permian b}' Peale, the thickness becomes more normal, viz. 1,500 to 1,800 feet; and if 

 we can grant that the lower part of the Permian of this same section, whose upjjer part 

 has been joined with the Triassic, is not really the equivalent of the Permian of the 

 upper Eagle River section, but lai'gel}- overlies it, the equivalent of the Maroon will 

 be increased from 3,600 to 4,300 feet. It is objectionable to depart from the author's 

 grouping of these beds, but b}' doing so in this case greater uniformit}' in the lithol- 

 og3' and thickness of the different formations is attained. Peale himself has made 

 equally wide departures in his summarized section published in the annual report for 

 1875, appai'ently with the object of bringing this section into a closer agreement with 

 those of other areas. In this section he refers 500 feet at the base to the Eocar- 

 boniferous. This division is clearly that to which a thickness of 1,000 to 1,500 feet 

 was earlier given, and which was doubtfuU}^ refei'red to the Devonian (beds 25 and 

 26). The Coal Measures division of the summarized section comprises without doubt 

 beds 1 to 23 of his early Cai'boniferous section (section No. 2, page 115). To the 

 Permian of the summary section a thickness of 2,000 feet is ascribed, while of the 

 earlier Permian sections one has 1,500 feet and the other 1,276 feet. The upper por- 

 tion of the summarized section evidentlj^ corresponds to the top of the Permian of the 

 lower Eagle River section. The increase of 500 feet in the later reference must have 

 been arbitrarily made, or else have been justified by adding to the base of the section 

 on the lower Eagle River some portion of the Permian of the upper Eagle River 

 section. This is the course which I have allowed myself in the foregoing discussion. 

 14361^No. 16—03 5 



