232 EDWARD B. MATHEWS 
the granites of the Cripple Creek type in a manner well shown 
near the mouth of Arequa Gulch a few miles below the town of 
Cripple Creek. On the west the contacts with the gneissic 
granite are generally obscure, though the finer grained may be 
seen cutting the coarser and more schistose rock in Caylor 
Gulch at an elevation of 8600 feet. 
The manner of weathering and the resulting physiographic 
forms are intermediate between those of the Pikes Peak and 
Summit types. The hills are neither so smooth, so bold, nor so 
massively jointed as those composed of Pikes Peak granite; 
while the disintegrated fragments are not as compact and angu- 
lar as those of the Summit type. The mineralogical changes 
are those common to granitic minerals. 
FINE GRAINED TYPE 
The rocks included under this head do not occur in well- 
defined masses extending over large areas but in small dikes dis- 
tributed throughout the entire area studied. Nor are they so 
closely allied in their mineralogical and textural features as 
members of the preceding three groups. Their correlation is 
based upon their composition and texture, mode of occurrence, 
age, and present topographic position rather than upon their 
areal continuity. All of these rocks are fine grained hypidio- 
morphic granular aggregates of reddish color, composed of 
quartz, feldspar, and one or both kinds of mica, with small 
amounts of microscopic fluorite, magnetite, epidote, zircon, and 
apatite. 
The color of these rocks varies from brilliant red to pinkish- 
white or dull yellow, but is usually bright pink. In the latter 
case the feldspars are stained by finely disseminated iron oxide. 
The size of the individual grains is very constant, and rarely 
exceeds one sixteenth of an inch. Among the individual con- 
stituents there are several points of difference from the same 
minerals in the earlier types. Quartz is more abundant and in 
grains as large or larger than those of microcline, while incipi- 
ent granulation shown by a mottled extinction is more frequent. 
