14 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
12° Dolomite; essentially like No; W0ys2 fase Ss. e e S eee ee ae ese ee 8 feet. 
13. Like No. 12 in structure, but blue or brown in color, and containing occasional sand 
PTAINS 2-2. e-\sud Sonh sates SP cas tee Serie eee a oS EEN. tesa tee erie 12 feet. 
14. Hard, white quartzite, weathering yellow-brown________-___.___. _--..__-.-_-__-- 2 to 4 feet. 
15. Sandy, brown, crystalline dolomite, fine grained, with frosty luster, passing upward 
into the dark-blue dolomite of the Carboniferous ._-___--.---...-------------.------ 10 feet. 
On the south-facing cliff of Castle Butte, which overlooks Queens © 
Gulch, the beds of the Parting Quartzite series are also exposed in their 
full thickness. Here the examination made was not so detailed, but in a 
general way the series consists of a basal impure quartzite, a shaly bed 
stained a deep-maroon color, a heavy, light-green lithographic dolomite, 
and at the top of the series a heavy quartzite. The thickness of the section 
in both places is nearly the same, namely, about 60 feet. 
The quartzites at the top and the bottom of the series, the gray, light- 
green, or light-brown massive lithographic dolomite, and the dark-brown 
shaly beds are the characteristic features of this horizon in the Aspen 
district, and are nearly always present, although the minor stratigraphy 
varies considerably, so that the detailed section of the beds on East Aspen 
Mountain is probably only local and might not hold good for any other 
part of the district. On account of the prevailing colors of the chief 
members of this series, they are known in Aspen as the gray, the green, 
the maroon, and the white beds, the gray and the white being chiefly the 
quartzites, the green the lithographic dolomites, and the maroon the high- 
colored dolomitic shales. The series may be summed up as broadly 
characterized by an impure feldspathic quartzite at the base and a heavier 
and purer quartzite at the top, with an intermediate series of massive litho- 
graphic dolomites and shaly dolomites. The shaly dolomites are richly 
colored, chiefly brown and green; the colors are sometimes solid, oftener 
banded, mottled, or arranged in rings. 
Microscopic structure of the basal quartzite —In appearance the basal ‘quartzite is 
quite ordinary, being light gray, light green, or pure white in color. In 
texture it is sometimes uniform, but oftener incloses grains of different. sizes, 
varying from the minutest dimensions up to an eighth of an inch in diame- 
ter. It is also remarkable for carrying bands or blotches of the gray 
lithographic’ dolomite into which it passes above. Under the microscope 
there are found, besides the quartz, detrital grains of feldspar, chiefly 
microline, and subangular or rounded fragments which are made up of 
interlocking crystals of carbonate and are evidently detrital fragments of 
