70 CAKBONIFEBOUS FORMATIONS AND FAUNAS OF COLOKADO. 



The Paleozoic geologic soction in the C'i'c'stcd lUitlc quadrangle, as givcTi in the 

 Anthracite-Crested Butte Folio, is as follows: 



Paleozoic section in Crested Butte quadrangle. 



.TURATIilAS. 



Feet. 

 Gunnison formation: The upper two-thirds drab, green, yellow, and jjink clays, with thin 



limestone. The base is a heavy white ipiartzite .350-500 



CARBONIFEROUS. 



Maroon conglomerate ( upper portion ) : Conglomerate and sandstone in heavy beds. The 

 material chiefly derived from the Archean and jjartly from the earlier Carljoniferous beds. 

 Occasional thin beds of fossiliferous limestone 2, 500 



Maroon conglomerate (lower portion) : Quartzose conglomerate, grit, and sandstone with 

 varying amount of pebbles derived from the Carboniferous, which sometimes form the bulk 

 of the deposits. Color yellowish gray. There are thin, interbedded limestone layers. 

 These and the limestone pebbles are fossiliferous 2, 000 



Weber limestone: Dark gray to black shale, with thin limestones carrying black chert 100-550 



Leadvdlle limestone: The upper third massive, blue, and cavernous. The lower two-thirds 



bedded, gray to brown. Dark cherts 400-525 



SILURIAN. 



Yule limestone: At the top, 80 feet of green, pink, and yellow shale and thin limestone. The 

 middle portion massive gray limestone with white chert. Lower portion white quartzite 

 75 to 100 feet thick 350-450 



CAMBRIAN. 



Sa watch quartzite: The upper two- thirds red quartzite containing glauconite. The lower 



two-thirds quartzite with conglomerate at the base; pebbles of white quartz 50-350 



ARCHEAN. 



Granite, gneiss and schist. 



An unconformitj' is indicated at the base of the Sawatch quartzite, another 

 between the Weber and Leadville limestones, and a third at the top of the Maroon 

 conglomerate. 



The geologic sequence in the Crested Butte quadrangle appears to be in the 

 main very similar to that at Aspen which I have discussed on the pages devoted to 

 the Grand River region; and as the most probable correlation between tlie two is 

 Indicated b}' the nomenclature employed for the formations of the two sections, as 

 well as in the text of the monograph, no discussion on my part is called for except in 

 one or two instances. Spurr found that in his area the Cambrian and the Silurian 

 beds became thicker toward the south, but, contrary to what one would expect from 

 this, the Cambrian of the Crested Butte cpadrangle is thinner than that of the Aspen 

 region. The Silurian, however, js a trifle thicker. The combined thickness of these 

 formations appears to be about the same in both areas. 



