EESTTME OF LITERATURE. 



53 



Section at Aspen. 



Feet. 



Trias. 



;00 



2,600 



Carboniferous 



Devonian (?) 

 Silurian 



Cambrian 



Granite. 



'Gunnison formation: A gray or yellow basal sandstone, often calca- 

 reous, overlain bj' reddish, grayish, or ^-ariegated shaly sand- 

 stones 



Red sandstones: Light-red sandstone, mdre or less grading into the 

 darker beds below 



Maroon formation: Impure grits, and thin-bedded, shaly limestone; 

 calcareous and thin bedded at first, but more massive and arena- 

 ceous above; in color, a peculiar dark red 4, 000 



Weber formation : Thin-bedded, carbonaceous limestones and calca- 

 reous shales; the typical rock a black limestone; separated from 



the Leadnlle limestone by a distinct plane 



Lead ville limestone: Above, a massive blue limestone 100 to 150 feet 

 in thickness; below, a heavy, hard, gray-blue dolomite, with some 



chert : thickness from 200 to 250 feet 



(Parting quartzite: This formation consists of thin beds of quartzite, 



I sandstone, dolomitic shale, and dolomite 



I Pure dolomites of a light gray-blue color, with some chert; the thick- 



l ness varies from 250 to 400 feet, thickening southward .' 250-^100 



A fine white quartzite, conglomeratic at the base; the upper third is 

 dolomitic, sometimes glauconitic, and it graduates above into the 



pure dolomites of the Silurian 200-400 



Like the latter, this formation thickens to the southward, where it 

 measures from 350 to 400 feet. In the north its thickness is 200 

 feet or less. 



1, 000 



50 



67 



Besides the unconformity which is hinted at between the Lead ville and Weber 

 formation.s, Spurr mentions an important one which occurred at the close of the 

 deposition of the red Triassic sandstones. "This break," he says (page 43), "was 

 probably accompanied by a considerable uplift, for the succeeding beds of the 

 Gunnison foi'mation, which are of late Juratrias age, are probably of fresh-water 

 origin. In the interval between the deposition of the red sandstones and shales 

 there was probably some folding and perhaps a great amount of erosion. The red 

 sandstones appear to be missing in part or wholly in certain areas which closely 

 adjoin the Aspen district." 



The determination of the age of the Paleozoic beds is not based directly upon 

 paleontologic evidence, for apparently fossils were not collected except in a few 

 instances, but upon correlation with formations in areas near by whose age is more 

 or less well established. From the Leadville limestone a lumiber of foraminiferal 

 types are mentioned, none of which, however, have come into my hands." They are 

 of little importance in determining the age of this formation, which should without 

 doubt be placed in the Lower Carboniferous. The Devonian age of the Parting 

 quartzite depends upon some scanty and imperfect fish remains, and though this 



a Lakes cites from this formation at Tourtelotte Parle Syringoporaf Zaphrentis, jPleitrotomaria, and Straparollus, and from 

 Fryingpan Creelc, Straparoltus and Euoviphalas. Tliese fossils are among those studied by me and are referred to in the 

 paleontologic section of this report (Colorado State School of Mines, Bienn. Kept, for 1886, 1887, p. 00.) 



