88 
:niE GRAND GAifON DISTRICT. 
lower Silurian, and their contact with the Carhoniferons is unconformable, 
both by dip and by erosion. In the upper })art of the palisades which form 
the wall of the upper chasm we find at the summit two series of limestones, 
'fhe upper contains an abundance of siliceous matter, one portion of which 
is intimately disseminated throiigh the mass while another portion is aggre- 
gated into myriads of cherty nodules varying from two to ten inches in 
diameter. The lower one is a purer limestone with few nodules. The 
cherty members form a nearly vertical band at the summit of the wall; the 
purer membei’s form a Man.sard slope beneath, covered with talus. The total 
thickness of the limestones is about 700 to 750 feet. Beneath them come 
sandstones a little more than 250 feet thick, which form everywhere a ver- 
tical plinth or frieze. They are very adamantine in texture, and one of the 
members, about 180 feet thick, is in every exposure seen to be uniformly 
cross-bedded. Under the cross-bedded sandstone is a mass of thinly bedded 
and almost shaly sandstones, having an aggregate thickness very closely 
approximating to 1,000 feet. They are of an intensely brilliant red color, 
but are, in greatest part, covered with a heavy talus of imperishable cherty 
nodules, fragments of the cross-bedded sandstones, and spalls of limestone 
shot down from above. The color of these is pale gray, with occasionally 
a yelloAvish or creamy tinge. The brilliant red sandstones form the long 
curved slope which descends from the plinth of cross-bedded sandstone to 
the plain below. 
The walls of the inner gorge have at the summit about 325 feet of hard 
sandstone of a brown-red color. Beneath the sandstone are about 1,800 
feet of impure limestone in layers of the most massive description Very 
]^G. 1. — Section of tbo Grand Canon at the foot of the Toroweap Valley. 1. Upper Aubrey; 2. Lower Aubrey; 3. Ked 
"VVall; 4. Base of the Carboniferous; 5. Lower Silurian and Archaean unconformable. Scale one mile to the inch. 
few such ponderous beds of limestone are found in any part of the world. 
The color is deep red with a purplish tone, but the brilliancy of the color- 
