48 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
rocks in the southwestern part of the district. But from the smaller amount of 
shearing and deformation which the Cripple Creek type has undergone, and from 
the presence in the Pikes Peak granite of innumerable dikes of a granite which is 
almost without question assignable to the Cripple Creek variety, the Pikes Peak 
granite may undoubtedly be considered the older. This was the conclusion 
reached by Cross and Mathews in a much larger field. No evidence as to the 
relative age of the Spring Creek granite was obtained. 
PEGMATITE. 
Closely related to the granites is pegmatite, which forms innumerable dikes or 
veins in various parts of the district. They are rather common in the Pikes Peak 
granite and locally occur in the gneiss, but only rarely cut the Cripple Creek granite. 
It is believed that most if not all of the pegmatite veins were a late phase of the 
•eruption which produced the Cripple Creek granite, for in several places, notably 
along the Florence and Cripple Creek railroad south of Hollywood, typical well- 
defined veins of pegmatite seem to grade directly into dike granite similar in 
character to that of the main mass west of Cripple Creek. 
The dikes are usually narrow and of red color, being made up principally of a 
potash feldspar with considerable quartz and smaller amounts of muscovite and 
well-crystallized magnetite. Occasionally the proportion of quartz is much greater, 
and the dike then may be mistaken for a quartz vein. Prospecting at several 
places has revealed their barren nature. 
An examination under the microscope of one of the more “graphic” of these 
pegmatites reveals abundant microcline, all arranged with the same orientation. 
Quartz, present in about equal amount, penetrates the microcline granophyricallv. 
Muscovite, often- showing beautifully its skeleton structure, is less plentiful and lias 
different orientation in different individuals. A few grains of magnetite are also 
present. 
GNEISS. 
Pocks of granitic texture, showing marked foliation, but no distinct banding,® 
occur at numerous places in the district. They belong to several varieties, but 
because of small and indefinite extent all but two have been omitted from the 
map. Of these two, both have been given the same color, since the mass on 
Calf Mountain is small and its origin is not absolutely certain. 
WOMACK GNEISS. 
The typ.e of gneiss which has the greatest development underlies most of the 
town of Cripple Creek and forms the ridge to the northwest. It also extends as a 
band averaging a third of a mile wide from the slope of Gold Hill westward beyond 
the boundary of the area shown on the map. A mass of similar character occurs 
on the ridge northeast of Cameron and there meets the Pikes Peak granite, but 
the nature of the contact is not well shown and the mapping of the rocks at that 
a The rocks thus described do not fall under the definition recently brought forward by Van Hise, who applies the 
term gneiss to a banded rock the bands of which are petrographically unlike one another. (Mon. U. S. Geol. Survey, vol. 
47, 1904, p. 782.) 
