GRANITIC ROCKS OF PIKES PEAK QUADRANGLE 221 
may apply, but the same phenomena may be the result of varia- 
tions in the conditions during solidification. With the less vis- 
cous state of the magma during the early stages of solidification 
the supply of material is abundant and the growth rapid. The 
imperfections in crystallization increase with the rate of consoli- 
dation, through the inclusion of interpositions and the imperfect 
filling of space. As the magma on cooling becomes more vis- 
cous, thereby decreasing the easy transfer of material and the 
consequent rate of growth, the molecular arrangement of acquired 
material on the growing crystal is more perfect in its outer zone. 
This difference in homogeneity between the core and exterior is 
sufficient to develop a tendency towards molecular rearrange- 
ment in the interior whenever the physical conditions are 
changed. The sharpness of the limits is determined by the 
growth lines as in twinning lamellae or zonal structures. 
Biotite occurs either as individual flakes or small aggregates 
presenting the appearance of single flakes to the unaided eye. 
The mica is strongly pleochroic in brown and yellow, and has 
an optic angle of 10° Since the plane of the optic axes was 
found in several instances to lie perpendicular to the leading 
ray of the percussion figure, much of the mica is probably 
anomite. 
Hornblende is relatively rare in all the granites of the area. 
It occurs most often in the Pikes Peak type associated with 
biotite and titanite. The amount of mica decreases somewhat 
when hornblende is present, while an increase in the latter is 
generally accompanied by an increase in the titanite. The horn- 
blende-bearing granites occur in somewhat circumscribed areas 
below Green Mountain Falls, along the railroad east of Florissant 
and in the hills east of Lake George. 
The accessory minerals enumerated on a preceding page 
occur in varying amounts. They are usually in small crystals, 
and belong to the earlier stages of consolidation. Titanite and 
fluorite are of especial interest, since the former has been found 
only in this type while the latter is rare, though abundant in the 
Summit type. Neither presents any mineralogical peculiarities. 
