ASPEN DISTRICT MAP. 147 
great throw. They have an east-west trend and a dip to the south of about 
30 degrees. The phenomena along these faults tend to show that they 
originated previous to the ore deposition, but continued after it, so’ that 
they belong in a later system than do the Aspen Mountain faults, which 
appear to have been almost entirely developed before the cessation of this 
process. According to Mr. D. W. Brunton, who has made a careful study 
of the Della faults, about three-fourths of the movement occurred since the 
ore deposition. . 
Next in the order of development of faults seems to have come the 
Tourtelotte Park system, which has a north-south trend and a nearly ver- 
tical dip. The faults of this system have their greatest throw in Tourtelotte 
Park and diminish toward the north and to the south. They have appar- 
ently been developed entirely since the close of the ore deposition, and are 
therefore barren. 
Belonging to a slightly later date than the north-south Tourtelotte 
Park system are the east-west faults of Tourtelotte Park, which constitute 
the Butte system. This system, although probably it originated at about 
the same time as the north-south Tourtelotte Park faults, has apparently 
had its greatest activity at a slightly later period, and some of its faults 
have developed entirely in post-Glacial time. This is the most recent of 
all the fault systems, and the disturbance is still going on. Most of the 
other faults in the systems previously enumerated are still moving slightly, 
but not to such great extent as the Butte system. The universal motion 
shows, however, that the Tourtelotte Park uplift is still slowly progressing. 
Cause of uplift—'The most interesting feature in the structure of this 
district is the local uplift which has caused the formation of numerous 
faults, and, indirectly, of the ore deposits, for along these faults the ore- 
bearing solutions have circulated, and there they have deposited their load. 
This uplift is purely local and has no apparent reference to the structure in 
the surrounding rocks. It does not seem probable. therefore, that it has 
been formed by regional stress or by any lateral thrust, but is such as 
might be formed by a vertical push from below by some restricted force. 
The period at which its formation began was one of intense eruptive 
activity. Immediately previous the diorite-porphyry and quartz-porphyry 
were intruded into the sedimentary rocks. The diorite-porphyry has been 
shown to be probably an outlying sheet connected with the main dioritic 
mass of the Elk Mountains, while the quartz-porphyry has apparently 
