435 
MINES OF BATTLE MOUNTAIN, EAST GROUT. 
from the old crater, to the sorting of particles by rolling down slopes, or to slight 
difference in size of the comminuted fragments thrown out by successive volcanic 
explosions. 
The contact between the granite and breccia is an irregular surface which 
plunges steeply down under the breccia to the north and east. Its dip is rarely less 
than 70°, is frequently approximately vertical, and in places forms what would be 
an overhanging cliff were the breccia removed. Some idea of the irregularity and 
general steepness of this contact may be had from PI. V (p. 26). As is there well 
shown, the granite in the Portland workings forms a bold promontory jutting into 
the breccia-filled funnel of the Cripple Creek volcano. Along the northern scarp of 
this promontory, west of the Portland mine, are the workings of the Granite, Dead 
Pine, and Ajax mines. Along the eastern declivity, south of the Portland, are the 
workings of Stratton’s Independence mine. 
The contact is well exposed on all the Portland levels from the 500-foot to the 
1,000-foot. As a rule it is sharp and readily determined. The breccia for a few 
inches from the granite is usually hard, rather fine grained, and, as shown by micro¬ 
scopic study, chiefly of granitic origin. It rests snugly against the rather minutely 
irregular wall of granite, which is not as a rule noticeably fractured or shattered. 
Usually there is no evidence of faulting along the contact, and there can be little 
doubt that the breccia was in the main originally deposited in the position it now 
occupies relative to the granite. Occasionally there has been some Assuring along 
planes adjacent and generally parallel to the contact. Such fissure planes, however, 
do not follow the irregularity of the actual contact and are not connected with any 
important faulting. 
On the 500-foot level a sharp contact between granite and breccia is well 
exposed in a short drift on the so-called Shaft vein, just west of the Burns shaft. 
The contact here is less steep than is common on the lower levels, dipping north at 
about 60°. It may also be well peen about 300 feet southeast of the Burns shaft in 
a crosscut east from the Portland vein. The contact is here ideally sharp, the breccia 
resting closely upon an uneven surface of granite. The dip is abnormally low, being 
only about 15° toward the east. This low dip is undoubtedly local, and if the 
breccia could be removed the granite at this point would probably be found forming 
a relatively flat bench or step, with steep scarps above and below. The contours of 
PI. XXVIII are strongly indicative of such changes of slope. 
On the 600-foot level the contact as exposed a short distance north and east 
of the Burns shaft is definite and close. It is rather irregular, but nearly vertical 
on the whole. Near the Diamond vein, however, about 300 feet east of the shaft, 
the contact is a regular plane dipping about 35° NE. and exhibiting clear evidence 
of some faulting between the granite and the breccia, but the movement is appar¬ 
ently local and not connected with any great displacement. The moderate dip, 
here as on the 500-foot level, prevails on the crest of the granite promontory. It 
is 20° steeper, however, than on the level above, which fact, taken in connection 
with what is known of the contact below, indicates proximity to the outer edge of 
the granitic bench already mentioned. 
On the 700-foot level the contact between the granite and breccia is exposed 
in the main drift about 100 feet north of the Burns shaft. It is here sharp and 
