great streams are formed.
Although the walls of the canyon are chiefly limestone, the adjacent
country is of red sandstone; and now the waters, loaded with these
sands, come down in rivers of bright red mud, leaping over the walls in
innumerable cascades. It is plain now how these walls are polished in
many places.

At last the storm ceases and we go on. We have cut through the
sandstones and limestones met in the upper part of the canyon, and
through one great bed of marble a thousand feet in thickness. In this,
great numbers of caves are hollowed out, and carvings are seen which
suggest architectural forms, though on a scale so grand that
architectural terms belittle them. As this great bed forms a distinctive
feature of the canyon, we call it Marble Canyon.

It is a peculiar feature of these walls that many projections are set
out into the river, as if the wall was buttressed for support. The walls
themselves are half a mile high, and these buttresses are on a
corresponding scale, jutting into the river scores of feet. In the
recesses between these projections there are quiet bays, except at the
foot of a rapid, when there are dancing eddies or whirlpools. Sometimes
these alcoves have caves at the back, giving them the appearance of
great depth. Then other caves are seen above, forming vast dome-shaped
chambers. The walls and buttresses and chambers are all of marble.

The river is now quiet; the canyon wider. Above, when the river is at
its flood, the waters gorge up, so that the difference between high and
low water mark is often 50 or even 70 feet, but here high-water mark is
not more than 20 feet above the present stage of the river. Sometimes
there is a narrow flood plain between the water and the wall. Here we
first discover mesquite shrubs,--small trees with finely divided leaves
and pods, somewhat like the locust.

_August 10.--_Walls still higher; water swift again. We pass several
broad, ragged canyons on our right, and up through these we catch
glimpses of a forest-clad plateau, miles away to the west.

At two o'clock we reach the mouth of the Colorado Chiquito. This stream
enters through a canyon on a scale quite as grand as that of the
Colorado itself. It is a very small river and exceedingly muddy and
saline. I walk up the stream three or four miles this afternoon,
crossing and recrossing where I can easily wade it. Then I climb several
hundred feet at one place, and can see for several miles up t