80 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
must be present. In the outcrops there is along the line of this section a 
decided diminution in the thickness of the formations, so that the distance 
between the granite and the Weber shales becomes abnormally small, and 
there appears to be no room for the Parting Quartzite or for the Leadville 
formation above it. In the underground workings, however, not only the 
Parting Quartzite but the Leadville dolomite ‘above is present, showing that 
it is not the Silver fault which has thus cut out the Parting Quarzite in 
outcrop. The way in which the Clark fault has probably produced this 
local narrowing of the outcrop is shown in the section, and the explanation 
is based on its actual movement as displayed in the Mollie Gibson and 
Smugeler workings. The downthrow of this fault on the west is shown in 
the sections as about 300 feet, but it will be remembered that the actual 
displacement is downward to the north on the west side of the steep, slip- 
ping plane, at an angle of about 30 degrees to the horizontal. Westward 
from the Silver fault to the end of the section there is nothing, besides the 
porphyry already described, but Weber shales and the sandstones, lime- 
stones, and erits of the Maroon formation. 
Section B—Section B, Atlas Sheet X, runs northwest from the summit 
of East Aspen Mountain across to the ridge at the northern termination 
of West Aspen Mountain, and so across Castle Creek into the Roaring 
Fork Valley and out of the area. 
At the eastern end of the section the beds are seen to have a shallower 
dip than at a little distance farther west. This shallowing of the dip is 
indicative of the approach to the anticlinal structure which has already 
been noted as sometimes occurring to the east of the main syncline. From 
the top of East Aspen Mountain the dip steepens steadily toward the west 
for a while, then suddenly flattens on approaching the bottom of the Aspen 
Mountain syncline. At the point where this steep dip of the eastern limb 
of the syncline changes to the flat dip at the bottom of the fold there are 
several slight slippings and faultings developed, of which the Aspen fault is 
the most important, and is the only one represented in the section. This 
fault has a slight downthrow to the east, not noticeable in this section; it 
probably runs into the Silver fault, and therefore its upper part is lost. 
The Silver fault is shown separating the porphyry from the Leadville 
formation, with a thin, variable band of broken shale between; the actual 
contact is between shale on the west side and the blue Leadville limestone 
