252 A OLA ORS a VA Sele Ans: 
canyons of streams tributary to the Arkansas River and by the recess 
or bay of Garden Park, nearly at the level of the plains. The princi- 
pal drainage of district 1s by tributaries of the Arkansas River, which 
flows through the Royal Gorge just beyond the southern boundary. 
The remaining drainage is into the Platte River, which cuts across the 
northwestern corner of the area in a deep canyon. 
The Colorado Midland Railroad traverses the district from east to 
west near its northern boundary. East of the center of the area is 
the mining district of Cripple Creek, reached by branch railroads from 
the north and south. 
General geology.—The granites of the mountains and plateau regions 
are reddish in color, coarse or fine grained, and similar to those of 
many other regions in Colorado. Of special interest is the observation, 
first made by the survey corps, that these granites contain many large 
-and small fragments of metamorphosed stratified rocks, quartzites and 
schists, belonging to the oldest series of sedimentary beds, the Algon- 
kian; and hence the granites are not of Archean age, as has previously 
been assumed. Most, if not all, of the gneisses in this district have 
been formed from the granites by a shearing strain, as is very clearly 
demonstrated in many places. 
The sedimentary formations of the area, and their characteristics 
of special interest, may be concisely referred to as follows: 
Algonkian.—Nearly 4000 feet of white quartzite, in small part con- 
glomeritic, is shown in the huge inclusion in granite in Wilson Park. 
These ancient strata are not known in this region except as inclusions. 
Silurian.—Three divisions of the Silurian strata, each about 100 
feet thick, have been recognized in Garden Park, and named respect- 
ively the Manitou limestone, Harding sandstone, and Fremont lime- 
stone. The Harding sandstone contains the oldest fossil fishes as yet 
known. Minor uncomformities separate these formations, and they 
are not known in so good development elsewhere. 
Carboniferous.—Resting on the Silurian is a thin limestone, called 
the Millsap, carrying a few Carboniferous shells, and known only in 
small remnants. The red sandstones and grits of Manitou and Garden 
Parks, 1000 feet in thickness, are considered as of Carboniferous age, 
and named the Fountain formation. No fossils are known in them. 
The strata of the Juratrias and Cretaceous have been found in 
remnants upon the granite plateau, indicating a former extension of 
these beds connecting with South Park. 
