PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 179 
District Pre-Cambrian Rocks 
Head of Canyon Creek Hornblende rock and schist 
Jerome Schist 
Grand Canyon Grand Canyon series, younger pre- 
Cambrian including over 4,700 feet 
of conglomerate, limestone, shale, 
quartzite, and sandstone resting 
unconformably on schist of older 
pre-Cambrian 
All the pre-Cambrian rocks in the foregoing sections excepting 
some of the Grand Canyon and northern Ancha sections are older 
pre-Cambrian. 
Richardson! finds that in the region of Castle Rock folio lying 
between Denver and Colorado Springs, only the youngest of the 
pre-Cambrian rocks of the Front Range, the Pikes Peak granite is 
exposed. 
Richardson? finds that the pre-Cambrian rocks of the Van Horn 
quadrangle of southwestern Texas are unconformable below the 
Cambrian and they consist of the following: 
Millicon formation—Fine red sandstone, cherty limestone, and conglomerate; 
: in northern Carrizo Mountains 
Relations concealed 
Carrizo formation—Quartzite, slate, and a variety of schists; in southern 
Carrizo Mountains 
Schultz? finds that the pre-Cambrian rocks of southeastern 
Idaho and western Wyoming include schists, granites, gneisses, 
and igneous rocks cut by dikes of pegmatite and diabase. Some 
of the schists and gneisses may be of sedimentary origin. The 
pre-Cambrian area lies in the central and eastern part of the Teton 
range. 
™G. B. Richardson, United States Geological Survey, Castle Rock Folio No. 198 
(1915). 
2G. B. Richardson, “‘Description of the Van Horn Quadrangle, Texas,” U.S. 
Geol. Surv. Geol. Atlas, U.S. Van Horn Folio (No. 194) (1914), 9 pp., 5 figs., 3 maps, 
illustration sheet. 
3 A. R. O. Schultz, “Geologic Reconnaissance for Phosphate and Coal in South- 
eastern Idaho and Western Wyoming,” U.S. Geol. Surv. Bull. No. 680 (1918), pp. 84, 
2 pls., 8 figs. 
