GRANITIC ROCKS OF PIKES PEAK QUADRANGLE 233 
Among the feldspars, microcline shows a slight increase in the 
size of its twinning network and the plagioclase a decrease in the 
size and abundance of its grains. Perthitic intergrowths are 
practically wanting in these rocks, whether fresh or altered, 
while micropegmatitic intergrowths are abundant, especially in 
the slides where the evidences of mechanical deformation are 
Fic. 9.—Fine grained type of granite. 
most numerous. The micas show no unusual features beyond 
the occasional inclusion of tiny individuals of fluorite showing 
well-defined crystal outlines in fresh flakes of biotite. 
Weathering. —The effect of atmospheric action on the fine- 
grained granites varies somewhat, but is ordinarily less pro- 
nounced than that on the other three types. When the rock 
disintegrates it usually falls into a mass of angular bowlders of 
small size, which are quite compact and sometimes covered with 
a surface glaze. This coating, which is faintly shown in Fig. 9, 
is much less clearly defined than is that on the Pikes Peak or 
