96 The American Geologist. February, 1902. 
THE AREAL GEOLOGY OF THE CASTLE ROCK 
REGION, COLORADO. 
Wiis T. Lee, Trinidad, Colo. 
PLATE IV. 
The Castle Rock region lies along the eastern slope of the 
Rocky mountains, south of Denver, Colorado. It is bordered 
on the north by the area known as the Denver basin, the geol- 
ogy of which is given in monograph No. 27 of the United 
States geological survey. The area over which my studies ex-, 
tended is shown in part in the accompanying sketch map 
(plate IV). It covers parts_of the Platte Canyon and Castle 
Rock quadrangles of the United States geological survey. 
For a distance of 30 or 40 miles east of the area mapped, only 
the younger formations, the Tertiary, appear at the surface. 
To the south of this area the Tertiary extends over the up- 
turned edges of the older sedimentary formations and lies in 
contact with the crystallines of the mountains for a distance of 
about six miles. Near Deadman creek the older formations 
re-appear. 
The geological formations of this region range from pre- 
Cambrian to Tertiary. With the exception of the youngest, 
the sedimentary formations are all more or less upturned 
against the mountains, the harder strata forming the “hog- 
backs” of the foot hills region. 
1.—Cambrian.—Near Deadman creek, six’ miles south of 
the area shown in the accompanying map, occurs a limited ex- 
posure of deep red _quartzyte about 25 feet thick. It rests at 
a high inclination on the eastern face of the front range of 
these mountains. In Manitou park, which lies west of this 
range, a few miles from the region in question, occurs a red 
quartzyte which Mr. Whitman Cross refers, though with some 
doubt, to the Cambrian.* The quartzyte at Deadman creek 
corresponds in character and stratigraphic position with the 
Cambrian quartzyte of Manitou park and may be of the same 
age. 
2.—Ordovician.—Above the red _quartzyte appears a series 
of cherty limestone layers interstratified with red clay. Brachi- 
opods from this limestone were submitted to Dr. Stuart Wel- 
*U. S. Geol. Sur., Pikes Peak Folio. 
