GEOLOGICAL STRUCTURE OF THE DISTRICT. 
27 
* 
of the Ajax drifts that have followed the contact far enough to the west, and is 
particularly conspicuous on the lower levels. A north-south section through the 
Ajax shaft, showing the steep dip of the contact, is given in fig. 63 (p. 479). The 
apparent flatter dip below level 6 is partly real and partly due to the obliquity of 
this part of the contact to the plane of the section. 
The breccia near the contact- contains abundant fine granitic detritus and fits 
snugly against a wall of granite which is far too irregular to be a fault contact. 
Blocks of granite from 2 to 3 feet in diameter are sometimes found in the breccia 
at a distance of 100 feet or more from the conduit wall. The contact is generally 
sharp and definite, though on account of the granite fragments in the breccia it is 
not everywhere conspicuous. The granite close to the contact is seldom brecciated, 
though in places considerably jointed and even shattered. 
In the Dead Pine mine, just east of the Ajax, the contact has been followed by 
an inclined shaft and found to dip north at 70°. The shaft of the Granite mine is 
in breccia, the various levels all running south across the contact into the granite. 
The general strike of the contact seems to vary from northwest to west, but as there 
are no drifts on it this point can not be accurately determined. The general dip is 
north at about 80°. The contact surface, however, is evidently very irregular, and 
there may be local southerly dips between levels 6 and 7 and between levels 9 
and 10. 
The Portland mine, north of Victor, affords better opportunities of studying 
the inclosing wall of the volcanic neck than any other mine in the district. The 
contact between the granite and breccia is an irregular surface which plunges steeply 
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. 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 Inde¬ 
pendence 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 hard, rather fine grained, and, as shown by microscopic 
study, is 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, how¬ 
ever, do not follow the irregularities of the actual contact and are not connected 
with extensive 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 
