ANCIENT CRYSTALLINE ROCKS-GRANITE. 
47 
Fluorite is present in sections from several localities and in a few instances 
appears to be primary, inclosing magnetite and tourmaline, penetrating individuals 
of quartz and occurring as sharp interstitial grains between perfectly fresh individ¬ 
uals of other minerals, and also included in feldspar. Cleavage is noticeable and the 
color ranges from colorless through pale pink to patches showing very deep purple. 
Traces of crystal form occasionally exist and minute fluid inclusions are sometimes 
observed. Although some fluorite, known to have been introduced into the granite 
through later fissures, occurs in much the same manner as above described, certain 
facts support the view that the mineral is in other cases an original constituent of the 
rock. Fluorine is known to occur in several minerals in the pegmatite veins which cut 
the granite of the peak. Moreover, Mathews’s descriptions of fluorite in the granites 
of the Pikes Peak quadrangle furnish almost convincing evidence as to its primary 
nature, and perhaps most conclusive of all is its distribution in remote and widely 
separated parts of the quadrangle, an area of nearly 1,000 square miles, and in locali¬ 
ties removed from vein mineralization. But it can be stated that within the limits 
of the Cripple Creek district primary fluorite is a rare constituent of the granites. 
Pyrite occurs in the granite near mineralized fissures, as in nearly all of the 
specimens from mine workings. Besides the epidote derived from the decomposition 
of biotite, this mineral sometimes occurs as faintly pleochroic aggregate patches 
scattered through the more decomposed rocks. Small areas of carbonate are occa¬ 
sionally seen, and hematite and limonite result from the weathering of magnetite. 
These rocks have the hypidiomorphic-granular texture of the typical granite. 
An interesting result of shearing of this granite is the production, along certain 
very narrow zones, of sericite and sillimanite. 
SPRING CREEK GRANITE. 
The Spring Creek type is not extensively developed, occurring only on the 
southwestern half of Red Mountain and on the hill to the south on the opposite 
side of Spring Creek. It is a bright-red, even-grained rock, containing conspicuous 
rounded grains of quartz 1 or 2 mm. in diameter. No specimen of very fresh 
material could be obtained. 
The color is found to be due to staining of the turbid feldspar grains with 
limonite. While orthoelase is probably the most abundant feldspar, the twinning 
of plagioclase is often seen, but further determination is impossible. Microcline 
is sparingly present and possibly a little microperthite. Quartz is abundant in 
clear grains which sometimes show related orientation when embedded in the feldspar. 
In a small dark fragment here and there and an occasional patch of secondary 
epidote, there is indication that a little biotite was originally present. Muscovite 
appears in the feldspar as small flakes, some of which have the same orientation 
and are parts of so-called skeleton crystals. Several small grains of fluorite were 
considered by Cross to be primary, but to the writer appear rather as of later age 
than the consolidation of the rock. 
RELATIVE AGE OF THE GRANITES. 
A 
Within the limits of the area mapped, little evidence as to the relative ages of 
the Pikes Peak and Cripple Creek granite is furnished by the contact of the two 
