118 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
outcrops at about the same elevation on the other side, which is also very 
steep, but is not well shown in the picture. Overlying the quartzite at the 
extreme left of the plate are the lowest beds of the Silurian dolomite, while 
underlying the quartzite and forming the base of both of the cliffs is 
granite. The main dip of the beds is not seen im this picture, being 
directly toward the observer, but the minor dips to the north and south can 
be made out in the cliffs on both sides. The top of the cliff at the right 
shows an outline against the sky corresponding with the attitude of its 
strata for a short distance north of its brow to the bottom of the little sag. 
Through this sag runs a heavy fault, to the south of which lies the granite, 
so that at the extreme right of the picture the outline of the hill has no 
reference to any stratification. 
The cliffs on the left side of this picture are better shown in Pl. XII, 
which is from a photograph taken from the hill on the south side, looking 
north across the canyon to the nearly vertical wall. On the extreme left 
of this picture is the same locality as the left side of the preceding plate, 
but the two pictures are, as explained, taken at right angles to each other. 
The abrupt cliff is made up of Cambrian quartzite, and the height of the 
cliff is very nearly the entire thickness of the formation. The changes 
of dip in these rocks may be well observed, and bring out the slight anti- 
clinal structure, for this is a natural cross section at right angles to the axis 
of greatest folding. In the central part of the picture the cliffs are nearly 
horizontal, as viewed in this east-west section, while to the west the dip 
grows steeper, until near the bottom itis 35 or 40 degrees. ‘To the east, 
on the other hand, the beds assume a very gentle easterly dip as far as the 
gulch which may be dimly seen through the trees at the right in Pl. XII. 
At this gulch the beds are cut out by the heavy fault before referred to, 
so that they abut directly against granite. Below the quartzite cliffs the 
rock is granite, while above them comes in the Silurian dolomite. 
The folding in the remainder of the area of the Lenado map is simple, 
and even monotonous, there being a continuous westerly dip from the 
western side of the slight anticline above described. Near the eastern end 
of the area the dip is flatter than farther west, the average at first bemg 
perhaps 30 degrees. This dip flattens on the tops of hills and steepens 
in the valleys, showing the persistence in the curving of the beds con- 
formable with the folding shown in the Cambrian quartzite in Pl. XI. 
