212 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
Creek fault in Queens Gulch a copious spring, which indeed is really the 
outbreak of an underground stream, rises between the Weber shales on the 
one side and the quartzite and dolomite on the other. In the Aspen mine 
the water which circulates along the Aspen and other faults comes down 
into the main Durant tunnel in a veritable waterfall, the roar of which can 
be heard a long distance away. These waters, which evidently come 
mainly from the surface, do not appear to exercise any dolomizing 
influence on the limestone which they traverse, and the phenomena of 
dolomization, silicification, and ore deposition along the faults show that 
the waters which produced them were in some way more potent than the 
cold waters which now circulate underground. 
DOLOMIZATION AT GLENWOOD SPRINGS. 
In this connection the waters at Glenwood Springs, which is 40 miles 
from Aspen, at the junction of the Roaring Fork and the Grand River, are 
highly interesting. The formations at the junction of the Roaring Fork 
and the Grand are the same as those exposed at Aspen. A short distance 
above the town of Glenwood Springs is the Archean granite, over which 
comes Cambrian quartzite, and then dolomite. The section was not care- 
fully measured, so that an accurate description of the deformation which it 
has evidently experienced can not be given. The Parting Quartzite, how- 
ever, was not found, and it is probably obscured by faulting. At the main 
springs, close to the town, the rock is pure blue limestone, like that at 
Aspen, and undoubtedly belongs to the same formation. The faulting 
which has been referred to is evidenced by many parallel vertical fissures, 
which are well exposed on the canyon walls. These become prominent a 
short distance down the river from the point where the granite outcrops; 
and are progressively more pronounced farther down. In the blue lime- 
stone on the walls of the canyon are great, vertical, irregular, open cham- 
bers, whose rounded walls show that they have been watercourses. In the 
immediate vicinity of the principal spring the disturbance has developed 
into a sheeting so prominent as to obscure the stratification. Along the 
fractures, for half a mile above the main spring, small springs of hot water, 
giving off sulphurous fumes, gush out at intervals. The one noted farthest 
up the river is in Cambrian quartzite. The open watercourses in the 
higher rocks have evidently been occupied by springs similar to these at a 
