18 
SURVEY OP TIIE COLORADO OP THE WEST. 
of about 1,800 feet. On the way we cross an abrupt monoclinal fold, 
the drops of which is to the east, and the total displacement about 1,400 
feet. At the foot of this canon we cross another of these folds, the drop 
ot which is to the east. Here we enter Marble Canon, a chasm cut 
through rocks of Carboniferous age. 
The course of the river is nearly south, and the dip as above stated, 
is to the north, so that at the foot we have passed through about 4,500 
feet of carboniferous rocks. In passing through Grand Canon we are 
going in the general direction of the strike of the beds, but there are 
great displacements due to faults, which, back from the river, are in 
many places monoclinal folds. The summit of the Grand Canon is every- 
where the summit of the carboniferous, which is from 4,000 to 4,500 feet 
in thickness ; but the gorge is sometimes more than 6,000 feet deep, and 
at these points we obtain a succession of sections of non-conformable 
shales, sandstones, and limestones, the greatest of which gives us a lit- 
tle more than 10,000 feet of beds. These are traversed by dykes of 
trap, or green stone, and irregular beds of the same eruptive material are 
found in places between these non-conformable rocks, and the overlying 
beds of Carboniferous age. Provisionally, I call these sedimentary 
rocks Devonian and Silurian. 
Still underlying these we find an extensive series of metaphoric crys- 
talline schists, in some places yet showing faint traces of the original 
stratification, but usually these are so degraded that the total thickness of 
the beds cannot be determined, or at least we were unable to do so. In 
places they constitute about a thousand feet of the altitude of the walls. 
These beds are traversed by dikes of granite, and beds of granite are 
found. I believe these beds to be intrusive, hence of igneous origin. 
In some places the evidence is complete. An extensive period of erosion 
sepai ates these schists and granite from the overlaying Silurian and 
Devonian rocks. 
In the Grand Canon we also have the records of an extensive period 
of deposition in the schists, followed by plication, erosion, Assuring, and 
eruption. Again we have an invasion of the sea, which remains until 
10,000 feet of shales, sandstones, and limestones are deposited; and this 
is followed by a dry-land period, marked in some places by at least 
10,000 feet of erosion, and accompanied by plication, Assuring, and 
eruption. 
Then follows another period, when the sea had dominion until the 
rocks of Carboniferous age and the Triass and Jura and the Cretaceous 
beds were deposited, and perhaps some Tertiaries; of this we cannot 
now be certain ; but at least 10,000 feet of beds were formed. All this 
is succeeded by a long period of erosion, in some places stripping off the 
whole 10,000 feet of later beds, and in the gorges, where the streams 
have made greater progress than the rains, channels are cut through 
the underlying rocks of Devonian and Silurian age, and still deeper into 
the schists and granite. 
