EE<APITLTLATION OF PALEOZOIC FORMATIONS. 173 



formation (which in this district is not very conglomeratic) of about 200 feet in 

 thicliness, the remainder being a dark reddish-brown, impure, micaceous sandstone. 

 The gray grits of this formation are made up almost wholly of granitic material, quai'tz, 

 feldspar, and mica. The red sandstones are ferruginous and contain more calcareous 

 and less granitic matt' rial. Spurr assigns to the Maroon formation a thiclvness of 

 4,000 feet, and to the l)rick-red sandstone overlying a thickness of 3,600 feet. 



The relation between the sections described by Spurr from about Aspen and that 

 of the Crested Butte i|uadrangle is not absolutely clear, although geographical h' the 

 two areas are not widi'ly separated. The Weber formation of the Aspen district 

 appears to answer to the Weber formation of the Crested Butte quadrangle, though 

 at Aspen its thickness is 'double what it seems to be in the Crested Butte quadrangle. 

 The Maroon formation appears in the Aspen district with characters considerably 

 changed. These seem to persist more uniforml}- throughout the series, in such a 

 manner that it no longer can be divided into two members, as in the Crested Butte 

 quadrangle. There ir is conglomeratic, e.specially in the upper portion: but this 

 character seems to be largely lost in the Aspen district. On the other hand, the 

 dark-reddish color, which is one of the distinguishing characters of the upper mem- 

 ber of the original Maroon, seems to pertain practically to the entire series about 

 Aspen. The Maroon at Aspen graduates into a bright-red series, the Triassic of 

 many authors, which ap|)ears to be unrepresented in the Crested Butte region. In 

 the one case the Maroon formation, in the other the Trias, is overlain by the Gunni- 

 son formation, whicii was preceded ))y an erosional unconformit}'. 



An argument might he constructed to show that the Maroon of Spurr represents 

 only tlie upper meinlicr of the tA'pical formation, but on the whole this seems too 

 improbable to requin- serious discussion. Unfortiuiately, the paleontol'ogic evidence 

 is not at hand to put tlii\sc matters lieyond dispute. 



While it is comparatively easy to see the general equivalence between Peale's 

 Eagle River section and the groups of rocks distinguished in the later monographic 

 and folio work, it is a little difficult to satisfactorily determine their corresponding 

 boundaries. 



In the Crested Biittc (juadraugle the Maroon formation is terminated above by 

 an unconformity, and inniiediateh' followed by the Gunnison formation, of Mesozoic 

 age. In the Aspen scctiou Spurr distinguished above the beds correlated with the 

 Maroon a series of bright-red sandstones referred to the Triassic. These are fol- 

 lowed by an unconformity, and then by the supposed equivalent of the Gunnison 

 formation. The beds which Peale counts as Jurassic appear to be same as the Gun- 

 nison formation of Spurr. and the latter's Leadville, Weber, and Triassic formations 

 would be comprised in the series Ijdng between iPeale's Silurian and Jurassic. 

 These Peale discriminates as possible Devonian, Carbonifei'ous, Pex-mo-Carlioniferous 



