LHP GRAND CANVON OF; THE COLORADO: 315 
Professor C. R. Van Hise gives a summary of the Algonkian 
rocks of the Grand Canyon of the Colorado, based upon the 
observations of Powell, Dutton, and Walcott. 
GEOGRAPHIC POSITION AND DISTRIBUTION, 
That portion of the Grand Canyon of the Colorado in which 
the Unkar and Chuar terranes and the typical section of the 
Vishnu terrane of the Algonkian (*) series or rocks are exposed, 
is situated in northern Arizona, between 36° and 36° 17’ N. 
latitude: and) Tit 47 .and) 112.05, W, longitude, Most 
of this area is in the valley portion of the canyon, between 
the mouth of Marble Canyon and a point south of Vishnu’s 
Temple, a little west of where the Colorado River changes its 
course from south to northwest. It is wholly within the greater 
depths of the Grand Canyon, east and southeast and south of 
the Kaibab plateau. The inter-canyon valleys of this portion of 
the Grand Canyon extend back from three to seven miles west 
of the river, and are eroded in the crest of the monoclinal fold 
that forms the eastern margin of the Kaibab plateau. All of the 
valleys have small lateral canyons that lead into them from the 
high margin of the plateau. The Chuar terrane is confined 
almost entirely to the inter-canyon valleys of Nunkoweap, Kwa- 
gunt, and Chuar, as shown on the map (Pl. VI.). About four 
miles below the mouth of the Little Colorado the Unkar strata 
rise above the river, and rapidly expand so as to form the inner- 
canyon beneath the Tonto sandstone for a distance of eleven 
miles down the westward bend of the river, south of Vishnu’s 
Temple. A small outcrop also occurs on the line of the Butte 
fault, at the lower end of Nunkoweap Valley. In going down 
the river the Vishnu rocks are first seen south of Vishnu’s 
lemple (GON: lat) Wiis si 30> Wealonge) sand! they appear 
to extend down the river to the southwestern side of the Kaibab 
plateau, nearly to Surprise Valley (lat. 112° 33’). Whether the 
pre-Tonto rocks near the mouth of the Grand Canyon are a 
portion of the Vishnu terrane is unknown. 
