ine, GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
zones in this mine, one at the Silver fault, in which the ore lay mostly in 
the blue limestone, and one at the Contact fault, in which the ore was 
mostly in the dolomite. 
The second Saddle Rock shaft is situated on Saddle Rock, between 
Keno and Ophir gulches. This shaft runs in altered limestone after 
passing through a slight thickness of Weber shales. Two levels from the 
shaft run east and cut the Sarah Jane fault only a short distance away, 
showing that the alteration of the limestone in the shaft is undoubtedly 
due to the proximity of this fault. According to these developments the 
fault is here vertical, or has a very steep dip to the east. 
Camp Bird shaft—T"he Camp Bird workings are situated on the outcropping 
eastern limb of the syncline, at a pomt where this fold has become very 
shallow. There is, therefore, no very great difference in the elevation of 
the workings, which are mostly on the Contact fault. The ore is mainly 
on the Contact fault, but follows certain definite zones, so as to make ore 
shoots lying in the fault. The most marked of these shoots runs northeast 
and southwest. It is cut off on the north side by the surface and on the 
south side by the Silver Bell fault, which separates this mine from the lowa 
Chief. This shoot has a variable width, averaging perhaps not more than 
100 feet. The ore is a softened and brecciated brown-stained limestone, 
having bowlders of typical blue limestone and also of frosty-lustered 
dolomite. Above this comes usually blue limestone and below it dolomite, 
the thickness of ore varying from a few inches to 30 or 40 feet. The 
shoot has, therefore, a northeast trend and a pitch of about 25 degrees to 
the north, with a restricted extent east and west and a comparatively slight 
thickness. Together with the inclosing formations it is displaced by an 
east-west fault which has a downthrust on the north side of about 50 feet. 
This fault is barren, but on following up the fault plane the continuation of . 
the shoot is found on the south side. The movement, therefore, came about 
subsequent to the mineralization. From here the ore shoot is traced con- 
tinuously southward to near the Silver Bell fault, where it is finally lost, 
being faulted away by the parallel slips which lie close to the Silver Bell. 
Another large ore body forms a so-called “chimney.” This is a 
nearly vertical shoot, which was followed up continuously from the Con- 
tact fault to the surface, ore being stoped out all the way. ‘There seems 
to be no definite lateral trend to this chimney. At other localities in the 
