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 depth of thirteen thousand feet--more than twice the present total depth of the canyon. The erosion of many thousands of centuries wore them away before the rocks that now compose the floor, the temples and the precipiced walls of the great canyon were even deposited in the sea as sand and limestone ooze, a fact that strikingly emphasizes the enormous age of this exhibit. Geologists speak of these splashes of Algonkian rocks as the Unkar group, another local Indian designation. There is also a similar Chuar group, which need not concern any except those who make a close study of the canyon. This is the picture. The imagination may realize a fleet, vivid impression from the photograph. The visitor upon the rim, outline in hand, may trace its twisting elements in a few moments of attentive observation, and thereafter enjoy his canyon as one only enjoys a new city when he has mastered its scheme and spirit, and can mentally classify its details as they pass before him. To one thus prepared, the Grand Canyon ceases to be the brew-pot of chaotic emotion and becomes the orderly revelation of Nature, the master craftsman and the divine artist. III