These broad canyons, or canyon valleys, are carved by the streams in obedience to an interesting law of corrasion. Where the declivity of the stream is great the river corrades, or cuts its bottom deeper and still deeper, ever forming narrow clefts, but when the stream has cut its channel down until the declivity is greatly reduced, it can no longer carry the load of sand with which it is fed, but drops 332 powell-canyons-206.jpg DANCE PARAPHERNALIA FROM TUSAYAN. OVER THE RIVER. 333 a part of it on the way. Wherever it drops it in this manner a sand bank is formed. Now the effect of this sand bar is to turn the course of the river against the wall or bank, and as it unloads in one place it cuts in another below and loads itself again; so it unloads itself and forms bars, and loads itself with more material to form bars, and the process of vertical cutting is transformed into a process of lateral cutting. The rate of cutting is greatly increased thereby, but the wear is on the sides and not on the bottom. So long as the declivity of the stream is great, the greater the load of sand carried the greater the rate of vertical cutting; but when the declivity is reduced, so that part of the load is thrown down, vertical cutting is changed to lateral and the rate of corrosion multiplied thereby. Now this broad valley canyon, or "box canyon," as such channels are usually called in the country, has been formed by the stream itself, cutting its channel at first vertically and afterwards laterally, and so a great flood-plain is formed. For a day we ride up the Paria, and next day return. The party in camp have made good progress. The boat is finished and a part of the camp freight has been transported across the river. The next day the remainder is ferried over and the animals are led across, swimming behind the ferryboat in pairs. Here a bold bluff more than 1,200 feet in height has to be climbed, and the day is spent in getting to its summit. We make a dry camp, that is, without water, except that which has been carried in canteens by the Indians. October 4---All day long we pass by the foot of the Echo Cliffs, which are in fact the continuation of the Vermilion Cliffs. It is still a landscape of rocks, with cliffs and pinnacles and towers and buttes on the left, and deep chasms running down into the Marble Canyon on the right. At night we camp at a water pocket, a pool in a great limestone rock. We still go south for another half day to a cedar ridge; here we turn westward, climbing the cliffs, which we find to be not the edge of an escarpment with a plateau above, but a long narrow ridge which descends on the eastern side to a level only 500 or 600 feet above the trail left below. On the eastern side of the cliff a great homogeneous sandstone stretches, declining rapidly, and on its sides are carved innumerable basins, which are now filled with pure water, and we call this the Thousand Wells. We have a long afternoon's 334