The oldest rocks of Arizona which form the precipitous walls of the inner or granite gorge of the Grand Canyon have never received the intensive study that has been given to their counterparts over the great northeastern plains of Canada, in the mountains of Scandinavia or on the rolling expanses of Finland. The metamorphosed rocks standing in places on end under the wedge of the Grand Canyon series of sediments (Algonkian) and elsewhere under the mantle of Paleozoic sediments are known as the Vishnu schist. To J.W. Powell these were known as the “Grand Canyon schists” of tentative “Eozoic” age. C.D. Walcott who proposed the term Vishnu from the occurrence beneath Vishnu temple in the Grand Canyon classified them as “bedded, sedimentary, unconformable, pre-Unkar (Lower Grand Canyon series) strata.
