GRAWNITIC ROCKS OF PIKES PEAK QUADRANGLE 223 
examined, but are shown in a general way in the maps of the 
early Hayden survey some miles to the north and east of the 
Pikes Peak area. Similar rocks have been described from the 
Platte Canyon in Jefferson county for the Educational Series of 
the United States Geological Survey." 
In its distribution the Pikes Peak type, in the contact with 
each of the three remaining types distinguished, appears as the 
older type. It is therefore the oldest granite in the area. The 
best place for studying the age of this type is in the region 
about the summit of the massif. Here it is cut by many dikes 
of the Summit type, which seem to radiate from the central 
eminence. The actual contact between the two granites is rarely 
evident in this area, however, as the blocks of the Summit type 
have formed a slide slope which masks the more easily dis- 
integrating coarse-grained granite. Wherever the contact is 
observable, as in Wilson Creek southeast of Cripple Creek, the 
finer rock is seen to cut the coarser. The relations with the 
Cripple Creek type are poorly defined, as the exposures almost 
always show small masses of metamorphosed sediments at the 
immediate contact. The, greater age of the Pikes Peak type ts 
shown, however, in several exposures, as, for example, on the 
north side of Caylor Gulch at an elevation of 8600 feet, where 
a fine-grained saccharoidal granite of the Cripple Creek type 
cuts the coarser schistose granite which is correlated with that 
onthe Pikes) Peak type. 
Weathering.—The processes and results of weathering in the 
Pikes Peak type are among its most characteristic features. The 
light pink color becomes darker on exposure and passes into a 
deep red through a bleaching of the biotite and the subsequent 
staining of the feldspars and quartz with the liberated iron oxide. 
The physical changes due to weathering are, however, more 
manifest. The rock disintegrates before it is decomposed. For 
this reason the hills are rounded and covered with granite gravel 
when the disintegrated material remains, and rugged or steep 
where the débris has been carried away. Fig. 2 gives a view of 
t Bull. U.S. Geol. Surv., No. 150, Washington, 1898, pp. 172-177. 
