GRANITIC ROCKS OF PIKES PEAK QUADRANGLE 239 
Among the elements represented, fluorine is of the most 
interest. Although small in amount the still smaller quantities 
of lime and phosphorus show that there is enough present to 
satisfy all of the latter even in the form of pure fluor-apatite, and 
much of the former in the form of fluorite. The possible excess 
of calcium is so small that the plagioclase plates must be sodium 
rich oligoclase and the perthitic pegs albite. 
The low percentage of iron and magnesium together with the 
strong pleochroism of the mica explains the relative scarcity of 
this mineral. 
The chemical analyses confirm the microscopic determina- 
tions and show that the general magma was of such a composi- 
tion as might produce a rock composed essentially of a potassium 
feldspar, perhaps intergrown with albite, and considerable quartz, 
with small amounts of fluorite and iron rich mica. 
RESUME 
The area included within the Pikes Peak quadrangle is a com- 
plex of granites, gneisses and schists overlain by numerous 
sedimentary and volcanic rocks of later age. The unaltered 
granites show, over an area of more than a thousand square 
miles, a notable uniformity in their mineralogical and chemical 
composition which is marked by the persistent presence of 
holocrystalline quartz-microcline aggregates bearing small 
amounts of equally constant biotite. On the other hand, these 
same rocks show a distinct diversity in the abundance, size, and 
form of their constituent minerals and the consequent differences 
in texture. 
The variations in texture and composition are as follows: 
Pikes Peak type-—Coarse granular to coarse porphyritic: 
rich in perthitic feldspar, poor in micropegmatitic intergrowths, 
and fluorite with occasional hornblende and titantite. 
Summit type — Granitophyric; poor in perthitic feldspars but 
rich in micropegmatite and fluorite. 
Cripple Creek type —Saccharoidal with rectangular feldspars ; 
poor in perthitic feldspars, micropegmatite, and fluorite. 
