436 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
close, rather irregular, and as seen in the drift nearly vertical. East of the Burns 
shaft the contact practically coincides with the No. 2 vein. 
On the 800-foot level the contact is in part the east wall of the No. 2 vein. It 
is sharp and irregular in detail. The granite is locally shattered for a foot or two 
from the contact, which is here nearly vertical. Toward the north the contact 
soon swings westward, away from the No. 2 vein, and is again well exposed in the 
main northeast crosscut about 125 feet from the Burns shaft. This contact is 
remarkably close and definite and shows no evidence of faulting. Its course where 
cut by the crosscut is nearly north and south, and it dips about 80° E. 
On the 900-foot level the contact between the granite and breccia is exposed 
in at least five places. North of the Burns shaft the granite shows some breccia- 
tion near the contact, and the latter is not so sharp and distinct as in other parts 
of the mine. Just east of the No. 2 vein, which is partly within the granite on 
this level, the contact is clearly exposed in a short crosscut. The granite is shat¬ 
tered, but not brecciated, for a distance of 2 or 3 feet from the breccia, while the 
latter contains abundant particles of microcline and some small fragments of granite, 
those seen being less than 3 inches in diameter. The contact here dips 75° to 80° 
E. A little farther north a crosscut west of the No. 2 vein, which is here wholly 
in granite, exposes a close, definite, irregular contact of the latter rock with the 
breccia. The dip of the contact here is practically vertical. 
On the 1,000-foot level the contact is exposed about 100 feet north of the 
Burns shaft and along the No. 2 vein. In general it is approximately vertical 
and presents characteristics similar to those observed on the level above. As pre¬ 
viously noted, the lodes are not deflected when crossing the contact. 
Intimately associated with the volcanic breccia and tuff are bodies of massive 
latite-phonolite and syenite. The latite-phonolite is usually a light-gray porphyritic 
rock showing small phenocrysts of feldspar and biotite. Its petrographical char¬ 
acter is described on pages 68 to 84 of this report. The rock, when unaltered, is 
readily distinguished underground from the breccia by its more angular fracture, 
greater hardness, crystalline texture, and, in one of the masses, by the presence of 
the black, sparkling scales of biotite, which do not so far as known occur in the 
volcanic breccia. The latite-phonolite is also far less generally impregnated with 
pyrite than the breccia. But notwithstanding these differences it is always an 
exceedingly difficult matter to determine the exact contact between the massive 
rock and the breccia, owing to the fact that the latite-phonolite is itself shattered 
or brecciated near the contact and locally mineralized with pyrite. When both are 
mineralized and altered, sharp distinction is seldom, if ever, possible between 
brecciated latite-phonolite, on the one hand, and a volcanic breccia containing 
abundant particles of similar rock on the other. There is nearly always a debatable 
zone from 10 to 100 feet in width which passes on one side into less shattered mas¬ 
sive latite-phonolite and on the other into a breccia containing, besides latite- 
phonolite, particles of quartz and microcline from the granite and sometimes of 
phonolite. 
The principal occurrence of latite-phonolite is in the northern part of the mine, 
in the vicinity of the No. 3 shaft, which is practically in this rock nearly down to 
the 1,000-foot level. It forms a large mass whose shape is only partly determinable 
