202 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
be derived from the trituration of sulphides. When richest it is nearly 
black, and is probably, in part at least, sulphide of silver with galena. 
The brown color is given by an admixture of yellow clay, which occurs in 
bunches and seams, and is of later origin. An assay of this yellow mud 
showed only 25 ounces of silver to the ton, while one of the blue-black 
material associated with it assayed 3,000 ounces. On both sides of the 
ore is brown altered limestone, which in places is brecciated and has frag- 
ments of soft black ore embedded in it. This ore, then, presents the char- 
acteristics of having been dragged into its present position. 
BIMETALLIC TUNNEL. 
The Bimetallic tunnel starts near the base of the Maroon sandstones 
and runs southeast across the Weber formation to the Lenado fault, which 
it crosses into the Leadville dolomite; farther on it goes through the Part- 
ing Quartzite into the Silurian dolomite. The information furnished by 
this tunnel is valuable chiefly as showing: that there has at least been no 
general mineralization along the Lenado fault. The fault has been thor- 
oughly explored in drifts from this tunnel and in raises and crosscuts, but 
was found to be absolutely barren, offering not even a trace of the precious 
metals in most places. It is well marked by a breccia of shale and 
dolomite. 
TILLY SHAFT. 
The Tilly shaft is situated in the gulch east of Silver Creek, which 
runs southwestward into Lenado Creek near the village. This shaft cuts 
the Silver fault, which here, as on Smuggler Mountain, separates the 
Weber shale from the Leadville dolomite. In this shaft some ore was 
encountered in hard blue dolomite. This contained considerable galena, 
but ran only about 5 or 6 ounces in silver. No ore was shipped from this 
mine, but the fact of its occurrence in this vicinity on the Silver fault is 
highly significant, especially as it seems to have formed in place. PI. 
XXIX is a view of the gulch up which the Silver fault runs, with the 
dump of the Tilly shaft near the center. 
RESUME OF LENADO GEOLOGY. 
In this district the beds have a generally westerly dip, which varies 
considerably in different localities. The chief displacement subsequent to 
the folding is that of the Lenado fault, which runs northeast and southwest, 
