se of grain, the product of swift currents of untold
thousands of centuries ago. This stratum makes a fine bright cliff
usually about four hundred feet in thickness, an effective roofing for
the glowing reds of the depths.

Immediately below the Coconino are the splendid red shales and
sandstones known as the Supai formation. These lie in many strata of
varying shades, qualities, and thicknesses, but all, seen across the
canyon, merging into a single enormous horizontal body of gorgeous red.
The Supai measures eleven hundred feet in perpendicular thickness, but
as it is usually seen in slopes which sometimes are long and gentle, it
presents to the eye a surface several times as broad. This is the most
prominent single mass of color in the canyon, for not only does it form
the broadest feature of the opposite wall and of the enormous
promontories which jut therefrom, but the main bodies of Buddha,
Zoroaster, and many others of the fantastic temples which rise from the
floor.

Below the Supai, a perpendicular wall of intense red five hundred feet
high forces its personality upon every foot of the canyon's vast length.
This is the famous Redwall, a gray limestone stained crimson with the
drip of Supai dye from above. Harder than the sloping sandstone above
and the shale below, it pushes aggressively into the picture, squared,
perpendicular, glowing. It winds in and out of every bay and gulf, and
fronts precipitously every flaring promontory. It roofs with overhanging
eaves many a noble palace and turns many a towering monument into a
pagoda.

Next below in series is the Tonto, a deep, broad, shallow slant of
dull-green and yellow shale, which, with the thin broad sandstone base
on which it rests, forms the floor of the outer canyon, the tessellated
pavement of the city of flame. Without the Tonto's green the spectacle
of the Grand Canyon would have missed its contrast and its fulness.

Through this floor the Granite Gorge winds its serpentine way, two
thousand feet deep, dark with shadows, shining in places where the
river swings in view.

These are the series of form and color. They occur with great regularity
except in several spots deep in the canyon where small patches of
gleaming quartzites and brilliant red shales show against the dark
granite; the largest of these lies in the depths directly opposite El
Tovar. These rocks are all that one sees of ancient Algonkian strata
which once overlay the granite to a dep