Bild EDWARD B. MATHEWS 
The rocks of the region represent massive and schistose 
granites, metamorphic schists, remnants of formations belonging 
to the Algonkian, Cambrian, Silurian, Carboniferous, Jura-trias, 
Cretaceous, and Eocene periods, and numerous igneous rocks 
including basic breccias, massive andesite, andesite breccias, tra- 
chyte, rhyolite, phonolite, and nepheline-syenite. 
The granites and gneisses of the Rocky Mountains have gen- 
Fic. 2.—Pikes Peak from carriage road (13,000), (showing gentler western slope). 
erally been regarded as part of the Archean complex, but it has 
been shown" that within the main granitic masses of the Pikes 
Peak area there are many included fragments of quartzite and of 
schists that show their derivation from sandstones through indu- 
ration and metamorphism. These sediments are regarded as of 
Algonkian age, and the granites cutting these strata are accord- 
ingly either Algonkian or early Cambrian. It is deemed most 
in harmony with the facts in the case to refer the granitic erup- 
tions to the late Algonkian period. 
The schistosity in the gneisses was produced prior to the 
Upper Cambrian and this fact, together with the assumed age of 
the granitic eruptions renders it probable that the squeezing 
t Pikes Peak Folio No. 7, Washington, 1895. 
