20 CONTRIBUTIONS TO ECONOMIC GEOLOGY^ 1913, PART I. 
systems in this canyon is exceptionally low. In the vicinity of the 
mines the lower 300 feet of the canyon is in granite, the walls rising 
steeply from the flat bottom. Extending back from the upper edge 
of the granite is a bench varying from less than 100 to 200 or 300 
yards in width. The floor of this bench, is the surface of the granite 
from which the overlying sediments have been removed. Immedi¬ 
ately back of the granite bench is a short talus slope formed from a 
soft shale overlying the granite, and above this rises a nearly per¬ 
pendicular wall of red sandstone. In the vicinity of the mines this 
sandstone is about 200 feet thick, but is said to attain a thickness of 
400 feet at some localities. On the top of the red sandstone is a 
second bench bounded by cliffs of gray sandstone, which was rnot 
examined, but which has a thickness of several hundred feet. 
The granite bench renders building of roads to the prospects 
relatively easy, as most of the prospects have been developed on this 
bench or but slightly above it, and few of the side canyons have been 
cut back across the bench to the base of the red sandstone cliff. 
GEOLOGY. 
IGNEOUS ROCKS. 
The district contains both igneous and sedimentary rocks. The 
basal formation is a granite that includes irregular blocks of mica 
and hornblende schist. The granite varies considerably in physical 
and chemical properties. Much of it is rather uniformly medium 
grained and is composed of feldspar, quartz, muscovite, and biotite, 
recognizable in the hand specimen. Under the microscope apatite, 
rutile, zircon, and magnetite are recognized as accessory minerals. 
The feldspar is mainly microcline but includes a little plagioclase 
near albite in composition. The muscovite is as a rule considerably 
more aboundant than the biotite, though there is considerable varia¬ 
tion in the mica content and in the relative proportion of the two 
varieties. 
At some places the granite is very much coarser, containing feld¬ 
spar crystals as much as an inch in greatest dimension. The coarser 
type appears to be more siliceous, quartz and pink feldspar being 
more abundant and the amount of mica being correspondingly de¬ 
creased. In one specimen examined microscopically titanite is rather 
abundant. Between the finer and coarser type there are apparently 
all gradations. 
The irregular bodies of schist inclosed in the granite are for the 
most part mica and hornblende schists, but some of them are very 
siliceous. 
The granite and schist are cut by a great number of pegmatite 
dikes, which range in size from a few inches to several feet. The 
dike rocks are usually very coarsely crystalline and are composed 
