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J. W. Powell - Canyons of the Colorado
interesting results have accrued.
CHAPTER XV. THE GRAND CANYON.
The Grand Canyon is a gorge 217 miles in length, through which flows a great river with many
storm-born tributaries. It has a winding way, as rivers are wont to have. Its banks are vast structures of
adamant, piled up in forms rarely seen in the mountains.
Down by the river the walls are composed of black gneiss, slates, and schists, all greatly implicated and
traversed by dikes of granite. Let this formation be called the black gneiss. It is usually about 800 feet in
thickness.
Then over the black gneiss are found 800 feet of quartzites, usually in very thin beds of many colors, but
exceedingly hard, and ringing under the hammer like phonolite. These beds are dipping and
unconformable with the rocks above; while they make but 800 feet of the wall or less, they have a
geological thickness of 12,000 feet. Set up a row of books aslant; it is 10 inches from the shelf to the top
of the line of books, but there may be 3 feet of the books measured directly through the leaves. So these
quartzites are aslant, and though of great geologic thickness, they make but 800 feet of the wall. Your
books may have many-colored bindings and differ greatly in their contents; so these quartzites vary
greatly from place to place along the wall, and in many places they entirely disappear. Let us call this
formation the variegated quartzite.
Above the quartzites there are 500 feet of sandstones. They are of a greenish hue, but are mottled with
spots of brown and black by iron stains. They usually stand in a bold cliff, weathered in alcoves. Let this
formation be called the cliff sandstone.
Above the cliff sandstone there are 700 feet of bedded sandstones and limestones, which are massive
sometimes and sometimes broken into thin strata. These rocks are often weathered in deep alcoves. Let
this formation be called the alcove sandstone.
Over the alcove sandstone there are 1,600 feet of limestone, in many places a beautiful marble, as in
Marble Canyon. As it appears along the Grand Canyon it is always stained a brilliant red, for
immediately over it there are thin seams of iron, and the storms have painted these limestones with
pigments from above. Altogether this is the red-wall group. It is chiefly limestone. Let it be called the red
wall limestone.
Above the red wall there are 800 feet of gray and bright red sandstone, alternating in beds that look like
vast ribbons of landscape. Let it be called the banded sandstone.
And over all, at the top of the wall, is the Aubrey limestone, 1,000 feet in thickness. This Aubrey has
much gypsum in it, great beds of alabaster that are pure white in comparison with the great body of
limestone below. In the same limestone there are enormous beds of chert, agates, and carnelians. This
limestone is especially remarkable for its pinnacles and towers. Let it be called the tower limestone.
Now recapitulate: The black gneiss below, 800 feet in thickness; the variegated quartzite, 800 feet in
thickness; the cliff sandstone, 500 feet in thickness; the alcove sandstone, 700 feet in thickness; the red
wall limestone, 1,600 feet in thickness; the banded sandstone, 800 feet in thickness; the tower limestone,
1,000 feet in thickness.
These are the elements with which the walls are constructed, from black buttress below to alabaster
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