PRE-CAMBRIAN NORTH AMERICAN LITERATURE 371 
rocks. The foregoing are cut by veins and dikes of crystalline rocks, both basic 
and acid. Resting unconformably upon the Archean rocks is the Belt forma- 
tion, which is supposed to belong to the Algonkian period. This formation is 
found on the western flank of the Bridger range. The rocks comprise sand- 
stones, conglomerates, slates, and arenaceous limestones. The series is about 
2500 feet thick within the area mapped. The Algonkian rocks are overlain 
conformably by the Cambrian Flathead quartzite. 
Eldridge,* from a geological reconnoissance in northwest Wyoming, finds 
that Archean granites, gneisses, and schists of various types form the crest 
of the Big Horn, Wind River, Absaroka, and Owl-Rattlesnake ranges. In 
the Wind River and Absaroka ranges the Archean areas are extensive. 
Resting upon the Archean rocks and in many places deriving material from 
them, are the rocks of the Cambrian system. 
Cross* describes and maps the geology of the Pike’s Peak sheet, The 
oldest rocks here found are Algonkian quartzites and allied rocks, which 
occur as fragments included in the granite. These vary in size from that 
shown in Wilson park to minor fragments. The Wilson park mass is nearly 
4000 feet in thickness, stands on end, and is exposed along the strike for 
about five miles. Other important masses of quartzite are in Cooper Moun- 
tain and Blue Mountain. These masses are cut by minute dikes and are 
entirely surrounded by granite. Smaller fragments are very numerous. 
Associated with the quartzites are certain gneisses and schists which almost 
grade into the quartzites, and probably represent metamorphosed Algonkian 
Strata. Schists also occur, especially in the Cripple Creek district, and these 
seem to represent earthy metamorphosed Algonkian rocks. Granites and 
gneissoid granites occupy much the larger part of the Pike’s Peak sheet. 
The more important granites are the coarse-grained Pike’s Peak type and a 
fine-grained granite. The gneissoid granites are but foliated phases of the 
granites, and between the two there are gradations. All the granites are 
cut by coarse granitic dikes and veins. The Silurian rocks rest unconform- 
ably upon, and derived fragments from, all the previous formations. 
Eldridge? maps and describes the Crested Butte sheet, Colorado, and 
finds that on the northwest and southeast corners of the district are Archean 
areas. These consists mainly of granite and granite-gneiss, with local devel- 
opments of gneiss and schist. 
"A Geological Reconnoissance in Northwest Wyoming, by GEorRGE H. ELp- 
RIDGE, Bull. 119, U.S. G. S., p. 17, with Geol. Map. Washington, 1894. 
?Geol. Atlas of the U.S., Pike’s Peak Folio, No. 7, by WILLIAM Cross, U. S. 
Geol. Sur. Washington, 1894. 
3Geol. Atlas of the U. S., Anthracite-Crested Butte, Folio No. 9, by GEorGE H. 
ELDRIDGE, U. S. Geol. Sur. Washington, 1894. 
