30 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
The general conclusion reached regarding this principal breccia mass, extending 
from Goldfield to Carbonate Hill and from Guyot Hill to Cameron, is that it occupies 
the throat of the main volcano. This is certainly true of the breccia between Gold 
Hill and Goldfield and between Victor and Altman. Whether the pit filled by this 
breccia is continuous with that north of Ironclad and Gold hills is not established, 
owing to the lack of deep workings at the head of Squaw Gulch. It may be that 
the schist mass of Fairview and the Granite mass of Bull Hill come together at a 
moderate depth and that the breccia of Globe Hill fills a separate vent, which only 
superficially coalesces with the great chasm to the south. 
Of the form of the outlying breccia masses, including those of Mineral Hill, 
Rhyolite Mountain, Copper Mountain, and Mount Pisgah, less is known. Though 
the breccia in some places, as just north of the city reservoir in Cripple Creek, seems 
to rest upon a surface of erosion, in most cases it has steep contacts with the older 
rocks, and appears to fdl local vents. On the east side of the Mineral Hill mass, for 
example, the. contact as shown by the Aztec shaft, 60 feet deep, dips 45° W. A 
steep dip is indicated also by the relation of the contact to the topography on the 
northeast side of the hill (PI. II). 
At the Fluorine mine, on Copper Mountain, the breccia rests on a gentle slope 
of granite, but contains great fragments of the underlying rock, showing that the 
source of the breccia is near. 
BRECCIA. 
LOCAL BEDDING. 
The general form and geological occurrence of the breccia have been partly 
outlined in the preceding section. The formation occurs mainly in the principal 
volcanic neck. There are, however, a few outlying masses, some of which seem to 
fill local volcanic vents, while others appear to be residuals of the formerly more 
extensive accumulations of breccia that lay upon the uneven surface of the pre- 
volcanic plateau. 
As a rule, the volcanic breccia is a structureless agglomeration of fragments, 
varying in the character and size of its constituent materials from place to place, 
but showing no stratification and no definite arrangement of its particles. There 
are a few notable exceptions to this rule, however. In parts of the Captain stopes 
and in the southwest part of the 220-foot level of the Portland mine the breccia, 
which in these places is rather fine grained, shows well-marked banding due to the 
alternation of layers of relatively fine and coarse material. On the 220-foot level, 
where these layers are best shown, they are about a foot in thickness and the mate¬ 
rial resembles nearly horizontally bedded grits or coarse sandstones. This bedded 
structure, however, is never continuous for long distances and the bands pass grad¬ 
ually into the usual unstratified breccia. Similar nonpersistent stratification occurs 
at a few places in Stratton’s Independence mine, in the southeastern drifts of the 
Isabella mine, in the Lucky Guss No. 2 mine, on the south slope of Bull Cliff, on the 
slope south of Cameron, and in the Elkton mine. A bed of very fine-grained, 
loose volcanic ash is exposed in the shallow Red Rock shaft near the Hoosier mine. 
In the Elkton the bands dip at about 40°. The lack of sharpness and persistency 
and the various attitudes in which this stratification occurs indicate that the sorting 
