(l8 OARBONIFEROITS FORMATIONS AND FAUNAS OF COLORADO. 



Apparently tho upper portion of Peale'.s .series, including the gypsum l)eds, is not 

 represented in Stevenson's section. Peale states" that the gypsiferous series on 

 Eagle River which Stevenson refers to the Carboniferous is the same which he him- 

 self reported as Permian or Pernio-Carboniferous. This can, however, hardly lie 

 the case, as Stevenson's gj'psiferous series is at the bottom of his section, while 

 Peale's is naturally at the top. The' thickness given by Stevenson, which amounts 

 to 5.000 feet, is greater than that of the corresponding beds in Peale's, Spurr's, or 

 Emmons's sections,'' and there is a more or less marked lack of agreement in detail 

 between his section and the others mentioned, though this is to be expected in all 

 save Peale's. Compared with the Aspen section, that given by Stevenson repi'esents 

 the Maroon formation, but at Aspen the Maroon is 4,000 feet thick and the calcare- 

 ous beds are chiefly confined to the lower portion, while Stevenson found them in 

 the middle portion and assigned to the whole a thickness of 5,000 feet. The series 

 which Stevenson divides into two great sandstones with an intermediate calcareous 

 group must apparently be correlated with the Weber grits and Maroon formation 

 of the Tenmile folio. In the latter their combined thickness is given as 4,000 feet, 

 while in Stevenson's section it is said to be 5,000 feet. Limestones appear to be 

 much more abundant in the Tenmile district than in the section at the forks of Eagle 

 River, and are especiall}- characteristic of the upper portion, in which, in the latter, 

 none were seen. This only proves, besides possibly a slight exaggeration in Steven- 

 son's measurements, the great variability in lithologic details from point to point of 

 this series of sediments. Stevenson has stated that the general description which I 

 have quoted above holds good for the great area surveyed by him. It is true that 

 the general features are very persistent and that the sequence almost everywhere 

 consists of a heavy hmestone bfelow and a great series of sandstones, with shales and 

 thin limestones, above. But the other points mentioned are not constant. Steven- 

 son usually seems to find, it is true, gypsum beds in the lower part of the sandstone 

 series, an occurrence not often mentioned by other geologists, but the abundance 

 and position of the limestone beds, uj^on which the subdivisions made b}' the latter 

 depend, appear to be features of great variability. 



Stevenson remarks upon the conglomerate which forms the downward termina- 

 tion of liis measured section on the forks of Eagle River that this bed is "some- 

 what altered, but in all other respects resembles the conglomerate seen at the head 

 of Taylor River." This expression evidently refers to the section in the Elk 

 Mountains described on page 365 of his report, where a conglomerate is recorded as 



aU. S. Geol. Geog. Surv. Terr., Ninth Ann. Eept., for 1875, 1877, p. 73. 



!)It Is more in agreement with the Maroon of the Crested Butte quadrangle, whicli measures 4,500 feet, though here 

 may be included probably inconsiderable portions of altered and unrecognizable Wyoming sandstone. Stevenson calls 

 attention to the similarity of the upper division of his Eagle River section to the upper division of that in the Sangre de 

 Cristo Range. The latter in its lithologic character strikingly resembles the upper Maroon of the Crested Butte district. 

 All three have the same thickness, 2,500 feet. (U. S. Seog. Geol. Surv. W. 100th Mer., Rept., vol. 3, Supplement, 1881.) 



