a4 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
‘Emmons! under the head of ‘Upper Coal Measures,” while Mr. Eldridge? 
has described it under the name of the ‘‘Maroon conglomerate.” Although 
the series in the Aspen region is not conglomeratic, yet its lithological 
peculiarities show conditions of deposition nearly similar to those of the 
corresponding rocks of the Crested. Butte district, and so the name “Maroon 
formation” has been adopted. Fossils discovered in these beds in various 
parts of Colorado show the whole series to be of Carboniferous age. Plant 
remains gathered by Dr. Peale® were referred by Professor Lesquereux to 
the Permian, while in the Tenmile district Mr. Emmons reports many fos- 
sils of Coal Measures types. In the Crested Butte district Mr. Eldridge 
found fossils in the limestone pebbles of the conglomerates which belong 
to the Coal Measures types. No fossils were found in this series in the 
Aspen district. 
The purplish-red beds pass upward into more massive and finer-grained 
sandstones, which are more purely siliceous in composition and of a bright 
brick-red color. This formation is well marked throughout a large part of 
the Rocky Mountain district, and although fossil evidence is very scanty, it 
has been referred by most geologists, on broad and general grounds, to the 
Triassic. The change to these red beds, however, is not abrupt, and does 
not indicate any break in the sedimentation. 
Description of the Maroon formation—'The oray calcareous member which has 
been taken as the base of the Maroon series is distinguished from the 
underlying rocks of the Weber formation chiefly by the absence of car- 
bonaceous matter and the greater coarseness of its materials. It is 
essentially a very impure limestone, becoming sandy and micaceous in 
bands. Its color is m general gray, which becomes yellow, brown, or red 
in spots and nonpersistent bands. In some parts there are found inter- 
calated green or blue thin-bedded limestones or calcareous shales. This 
eray bed is well marked from the vicinity of Smugeler Mountain northward 
to the limit of the Lenado special map. Its contact with the Weber shales 
is exposed in a knoll not far from the Smuggler shaft. It is shown in 
section in the Cowenhoven tunnel, and outcrops through most of the 
distance across the Hunter Park special area, near the road running from 
1Geology of Leadville: Mon. U.S. Geol. Survey, Vol. XII, 1886, p. 69. 
“Geologic Atlas U.S8., folio 9, Anthracite-Crested Butte, Colorado, 1894. 
%’ Annual Report of the Hayden Survey, 1873, p. 105. 
