The “inner gorge” of the Grand Canyon appears to have been cut far more rapidly than the outer one, and at a much later period; were this not the case there would be no inner gorge. It is a singular fact that some side canyons, the Kanab, for example, while now possessing no running water, or at best a puny rivulet, and depending for their corrasion on intermittent floods, meet on equal terms the great Colorado, the giant that never for a second ceases its ferocious attack. Admitting that the sharper declivity of the Kanab would enhance its power of corrasion, nevertheless we should expect to see it approach the Grand Canyon by leaps and bounds, like the Havasupai farther down, but, on the contrary, there are parts that appear to be at a standstill in corrasion, or even filling up, and its floor is a regular descent, except for the last three or four miles where the canyon is clogged by huge rocks that seem to have fallen from above. The maximum height of its present flood-waters is about six feet, proved by a fern-covered calcareous deposit, projecting some fifteen feet, caused by a spring (Shower-Bath Spring) on the side of the wall, seven or eight miles above the mouth, which is never permitted by the floods to build nearer the floor of the canyon. A suspicion arises, on contemplating some of these apparent discrepancies, that the prevailing conditions of corrasion are not what they were at some earlier period, when they were such that it was rendered more rapid and violent; that there was perhaps an epoch when these deep-cut tributary canyons carried perennial streams, and when the volume of the Colorado itself was many times greater, possessing a multiplied corrasive power, while the adjacent areas were about as arid as now. At such a time, perhaps, the Colorado performed the main work of the inner gorge, the Kanab, and similar affluents, their deep now rather evenly graded canyons. Such an increase of volume, if we suppose the aridity to remain as now, could have come about only by an increase of precipitation on the mountain summits. During the Glacial Epoch, the Rocky Mountain summits were considerably glaciated, the amount varying according to altitude and latitude. The general topography of the Colorado River was about as it is to-day, and the rainfall in the valleys probably nearly the same, or at least only a little greater. In other words, the conditions were those of to-day intensified. In summer, then, the amount of water seeking outlet by these drainage channels to the sea was enormously multiplied, and the corrasive power was correspondingly augmented. When the ice caps finally began to permanently diminish, the summer floods were doubtless terrific. The waters of the Colorado now rise in the Grand Canyon, on the melting of the snows in the distant mountains, from forty to one hundred feet; the rise must then have amounted to from one hundred to four hundred or more. The Kanab heads in two very