Beaver had not found a way into the valley by the trail of the cliff-dwellers, of that he was certain; and he began to have more than curiosity as to the outlet or inlet of the stream. When he passed some dead water, which he noted was held by a beaver dam, there was a current in the stream, and it flowed west. Following its course, he soon entered the oak forest again, and passed through to find himself before massed and jumbled ruins of cliff wall. There were tangled thickets of wild plum-trees and other thorny growths that made passage extremely laborsome. He found innumerable tracks of wildcats and foxes. Rustlings in the thick undergrowth told him of stealthy movements of these animals. At length his further advance appeared futile, for the reason that the stream disappeared in a split at the base of immense rocks over which he could not climb. To his relief he concluded that though beaver might work their way up the narrow chasm where the water rushed, it would be impossible for men to enter the valley there. This western curve was the only part of the valley where the walls had been split asunder, and it was a wildly rough and inaccessible corner. Going back a little way, he leaped the stream and headed toward the southern wall. Once out of the oaks he found again the low terrace of aspens, and above that the wide, open terrace fringed by silver spruces. This side of the valley contained the wind or water worn caves. As he pressed on, keeping to the upper terrace, cave after cave opened out of the cliff; now a large one, now a small one. Then yawned, quite suddenly and wonderfully above him, the great cavern of the cliff-dwellers. It was still a goodly distance, and he tried to imagine, if it appeared so huge from where he stood, what it would be when he got there. He climbed the terrace and then faced a long, gradual ascent of weathered rock and dust, which made climbing too difficult for attention to anything else. At length he entered a zone of shade, and looked up. He stood just within the hollow of a cavern so immense that he had no conception of its real dimensions. The curved roof, stained by ages of leakage, with buff and black and rust-colored streaks, swept up and loomed higher and seemed to soar to the rim of the cliff. Here again was a magnificent arch, such as formed the grand gateway to the valley, only in this instance it formed the dome of a cave instead of the span of a bridge.