214 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
bubbles up through fractures in the limestone. Most of these fractures 
are yellow, and apparently somewhat altered, while the rock a short distance 
away is perfectly blue and fresh. Four samples were selected for analysis, 
and the results are given below. No. 1 is the analysis of a specimen taken 
several feet from any fissure, which apparently had not been affected by 
circulating water. Nos. 2 and 3 were from the walls of different fissures 
along which water had flowed previous to the opening of the cave. No. 4 
consisted of broken fragments lying in the bottom of a cavity formed by 
the rising hot water. 
Analyses of rock from a cave near the Yampa Spring, Glenwood Springs, Colorado. 
No. SiOs. CaO. MgO. Fe,03. FeO. 
il . 06 55. 81 Trace. None. None. 
2 .28 55. 49 24 0.9 
3 222 55.17 21 Trace. 
4 21. 45 40. 64 73 .97 .23 
These analyses show a progressive change from the first, through the 
second and third, to the fourth, consisting in an abstraction of part of 
the carbonate of lime and its replacement by silica, carbonate of magnesia, 
and iron. This change is, then, a partial silicification, dolomization, and 
ferration now actually going on in the limestone at Glenwood Springs 
under the influence of ascending hot waters. 
A number of other analyses were made from samples selected from 
this locality, which all lead to ‘the same conclusion. In the Cloud Cave, 
which is a cavern in limestone some distance away from the springs, one 
sample was taken of the blue limestone forming its walls, and another of 
the limestone at the surface, a short distance away from the cave, but 
on the same horizon. No. 1 is the analysis of the sample from the cave, 
and No. 2 of the specimen taken from the outside. 
Analyses of limestone from and near the Cloud Cave, Glenwood Springs, Colorado. 
No. Si0b. CaO. Mego. FeO. FeO. | 
1 ~22 55. 45 24 . 10 . 10 
2 .11 | 55.68 Trace. .03 07 
