THE GRAND CANYON OF THE COLORADO. 313 
* 
been folded so many times, and so squeezed and heated, that 
their original structure as sandstones and shales is greatly 
obscured or entirely destroyed. Further, after these beds were 
deposited, after they were folded, and after they were deeply 
eroded, they were fractured, and through the fissures came 
floods of molten granite, which now stands in dikes, or lies in 
beds, and the metamorphosed sandstones and shales and the 
beds of granite present evidence of erosion subsequent to the 
periods just mentioned yet antecedent to the deposition of the 
nonconformable sandstones. 
In a report on the geology of the eastern portion of the 
Uinta Mountains, etc., 1876, page 70, Major Powell’s summary 
of the Grand Canyon Group is as follows: 
The Grand Canyon Group rests conformably upon the crystalline schists. 
The evidence of this is complete, for the lower sandstones and conglomerates 
first filled the valleys and then buried the hills of schistic rocks, and these 
conglomerates at the base of the group are composed of materials derived 
from the metamorphic hills about ; and hence metamorphism was antecedent 
to the deposition of the conglomerates. 
The plane of demarkation separating this group from the Tonto Group is 
very great. At least 10,000 feet of beds were flexed and eroded in sucha 
manner as to leave but fragments in the synclinals. Then followed a period 
of erosion during which beds of extravasated material were poured over the 
fragments, and these igneous beds also were eroded into valleys prior to the 
deposition of the Tonto Group. 
Fossils have been found at the base of the Grand Canyon series, but they 
are not well preserved and little can be made of them. Still, on geological 
evidence, I am of the opinion that these beds should be considered Silurian. 
The subjacent Grand Canyon schists are referred to the 
Eozoic. This is followed by a statement that the grouping 
should be considered merely tentative; that it may need some 
modification, or possibly radical changes. 
When describing the unconformity between a horizontal series 
of rocks forming the upper 4000 feet of the canyon walls and 
the subjacent unconformable series, Captain C. E. Dutton stated, 
in his Tertiary History of the Grand Canyon District, 1882, page 
179, that the thickness of the lower series must be very great-—— 
at least 6000 feet, that Major Powell’s estimate of 10,000 feet is 
