178 EXPLORATION OF THE CANONS OF THE COLORADO. 
mountain is composed of sedimentary beds, and the summit of this, cooled 
lava. So even, these so called eruptive mountains were not piled up, but 
were carved from beds of sedimentary and igneous matter. 
We have named this group, in honor of the Secretary of the Smith 
sonian Institution, ''Henry Mountains." 
A few miles below the mouth of the San Juan River we come to an 
interesting monoclinal fold, where the dip of the rocks is in a direction a 
little north of east; that is, the beds are dropped down on the eastern side 
of the line, which trends nearly north and south, not broken off and 
dropped down, but flexed, or bent, so that the beds on the western side of 
the line are found at an altitude many hundreds of feet above those on the 
east, and farther down the river the rocks exposed at the water edge are of 
greater age than those above. 
Hereafter, in this discussion, I shall more fully explain the nature of 
these monoclinal folds and faults, and the topographic features to which they 
give origin. 
At the foot of this canon another monoclinal fold is seen, with the 
throw, or drop, also on the east side, or the uplift, if one is so pleased to 
term it, on the west side; and this brings up again Carboniferous sandstones 
and limestones. The surface of the country immediately outside the canon, 
along its whole course, is on the summit of the red Trias; but, away back 
on either side, we see long lines of towering cliffs, now running in this, now 
in that direction, still keeping their courses parallel to the axes of folds which 
are scattered in many directions over the country. A region more desolate, 
and, for all economic purposes, more valueless, perhaps, cannot be found on 
the continent. 
There are some features of this canon of great interest, which I have 
already mentioned in the account of the exploration. These are the cham 
bers, or caves, found along the canon, at the foot of the wall, here and there, 
or in the side canons and gulches ; the great mural cliffs, about sweeping 
curves of the river; terraced glens, where the walls are composed of well 
denned strata, with springs about which oaks and aspens grow; and the 
deep, narrow alcoves or side gulches. 
The origin of these chambers was explained in the mention of Music 
