THE GRAND CANYON OF THE COLORADO, a7 
CAMBRIAN. Tonto. 
Unconfornuty.—— 
| Chuar. 
ALGONKIAN. Grand Canyon. : 
|] Unkar. 
—— Great Unconformity — 
ALGONKIAN (7?) Vishnu. 
STRATIGRAPHIC RELATIONS. 
The stratigraphic relations of the Cambrian, Algonkian, and 
the doubtful Vishnu beds are indicated by the preceding tabula- 
tion, and are clearly shown by section A—A’ of the map. 
Within the Algonkian series there is no recognized interruption 
in sedimentation between the base of the Unkar terrane south of 
Vishnu’s Temple and the summit of the Chuar terrane at Nunko- 
weap Butte, with the exception of a slight unconformity by ero- 
sion at the summit of the Unkar terrane. At the base of the 
Unkar terrane there is a bed of conglomerate that rests uncon- 
formably on the eroded edges of the indurated sandstones, mica- 
ceous schists, and granitic dikes. The unconformity is absolute. 
(lenges at), 
From the base of the Unkar terrane south of Vishnu’s Temple 
the strata dip 10° to the northeast, and then, as shown on the 
map (Pl. VI. and the accompanying section), they flatten out on 
the line of the divide between Unkar and Chuar Valleys, dip 25° 
to the north in the heart of Chuar Valley, and thence extend in 
low, broad undulations to the syncline of Nunkoweap Butte. 
North of the Butte the strata rise, the dip being from 20° to 25° 
southeast. The summit of the series is at Nunkoweap Butte, 
between Kwagunt and Nunkoweap Valleys. From the point 
south of Vishnu’s Temple to where the strata of the Chuar ter- 
rane pass beneath the basal beds of the Tonto sandstone, on the 
north side of Nunkoweap Valley, there is a marked unconformity 
between the strata of the Grand Canyon series and the superjacent 
