156 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
the Contact fault flattens out and runs into the Aspen fault. On the west 
side of this it becomes shallower, with a more northerly dip and a general 
east-west strike. The point at which the Contact fault runs into the 
Aspen fault naturally becomes lower toward the north, so that in the 
successive levels we find this poit constantly advancing. 
Besides the Aspen and the Contact faults there are, as in the Durant, 
a number of minor faults and cross fractures, which seem to be dependent 
upon and synchronous in origin with these greater faults. They are 
nonpersistent, often continuing but a short distance before running into 
one of the larger faults and disappearing. Along these faults, especially 
at their intersection, the ore is formed im immense and rich bodies. On 
account of the vertical position of the ore-producing zone, the mineral has 
been almost continuously stoped out down to nearly 1,500 feet below the 
surface, and it is claimed that for this reason the Aspen mine has been by 
far the greatest producer, in proportion to its surface acreage, among the 
mines of Aspen. 
Owing to their parallelism with the Contact fault, the ore shoots have 
a general dip to the east. The ore occurs indiscriminately im limestone or 
in dolomite, or in the Contact fault between the two, since immense stopes 
have been excavated in dense dolomite, while im other cases they lie 
entirely inclosed in blue limestone. But, as seén in the cross section, the 
ore bodies are, in a general way, confined to the fractured and sheeted 
zone where the beds have been overturned against the Aspen fault. 
The ore is practically the same as in the Durant mine, consisting in 
the lower levels principally of argentiferous galena with some blende. 
Most of it contains some barite. In the upper levels the ore has been 
oxidized, so that the metals occur chiefly in the form of carbonates and 
oxides. A peculiarly interesting type of ore was noted on the third level, 
near the shaft. This ore is to the eye a pure and apparently unaltered blue 
limestone, being hard and fresh. It contains no lead, and the silver is said 
to exist in small black: specks of sulphide. This ore is said to be high 
erade, running 200 ounces or more. On both sides of it there is barren blue 
limestone. In the Forest stopes, at about the second level, the ore also 
occurs with blue limestone on both sides, far from the solid dolomite, but 
in this latter case the ore is dolomized or has dolomite as a gangue, the 
dolomite being derived from the local alteration of limestone ; and as this 
