88 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO, 
Silver fault system —''9 this system belong a number of faults which are 
nearly or quite parallel to the bedding of the strata in which they occur. 
There are many of these found in nearly all of the formations in the district, 
but certain ones are so persistent and continuous that they can be easily 
traced for considerable distances. One of these faults, called the Contact 
fault, occurs between the blue Leadville limestone and the underlying 
dolomite. As far as can be seen, it does not cut across the beds, but runs 
strictly parallel to them, thus nearly always forming a true division between 
the two members of the Leadville formation. This fault has not been shown 
on the 800-foot map or in the 800-foot sections, but is found always at 
about 250 feet above the bottom of the Leadville formation. In the 300- 
foot sections made across the Tourtelotte Park mining map the Contact fault 
is shown, as determined by outcrops and mine workings. 
A still more important fault may be called the Silver fault. This 
oceurs at a horizon only about 150 feet, or often not more than 100 feet, 
above the Contact fault, and usually has, in this district, the blue Leadville 
limestone on one side and the soft shales of the Weber formation on the 
other. Developments in the mines show that there has been an immense 
amount of movement along this fault, resulting in the formation of a breccia 
made up of the limestone, shale, and porphyry, which is often as much as 
50 feet thick. It seems that the effect of this fault in the Tourtelotte Park 
district has been to reduce the thickness of the shale below the porphyry. 
From sections in other places it appears probable that there was an original 
thickness of about 250 feet of shale between the porphyry and the lime- 
stone, while in the Tourtelotte Park district there lies between the two only 
about 50 feet of shale, generally crushed and broken, and even this is 
sometimes wanting, so that the porphyry rests directly against the limestone. 
The Silver fault is shown in the 800-foot map and sections. It crops 
continuously on both sides of the main ridge to the west of Spar Gulch in 
TYourtelotte Park, dipping slightly into the hill east and west on either side 
with the strata which form the continuation of the Aspen Mountain syncline. 
Inasmuch, however, as this syncline retains its northerly pitch, which is 
steeper than the surface slope, the outcrop of the Silver fault becomes higher 
and higher, so that it finally passes above the surface, and is not found at all 
in the southern part of the district. The Contact fault, since it lies a short dis- 
tance stratigraphically below the Silver fault, persists a little farther to the 
