No additional information was obtained bearing on current theories of the causes that led the ancient occupants of the Mesa Verde cliff-dwellings to adopt this inhospitable and inconvenient habitat. It is probable that one and the same cause led to the abandonment of Spruce-tree House, Cliff Palace, and other Mesa Verde cliff-houses. The inhabitants of these buildings struggled to gain a livelihood against their unfavorable environment until a too-exacting nature finally overcame them. There are no indications that the abandonment of Cliff Palace was cataclysmic in nature: it seems to have been a gradual desertion by one clan after another. One of the primary reasons was change of climate, which caused the water supply to diminish and the crops to fail; but long before its final desertion many clans abandoned the place, and drifting from point to point sought home-sites where water was more abundant. All available data lend weight to a belief that the cliff-houses of Mesa Verde were not abandoned simultaneously, but were deserted one by one. Possibly the inhabitants retired to the river valleys, where water was constant, and later gave up life on the mesa. But even then the culture was not allowed to continue unmodified by outside influences. Where the descendants of Cliff Palace now dwell, or whether they are now extinct, can be determined only by additional research. Evidence is rapidly accumulating in support of the theory that the "cliff-dweller culture" of our Southwest was preceded by a "pit-house culture," the most prominent feature of which is the small circular or rectangular rooms, artificially excavated laterally in cliffs or vertical in the ground, which served this ancient people either as dwellings or for storage. The side walls of these rooms were supported in some instances by upright logs, and commonly clay was plastered directly on the walls of the excavations. The architectural survival of subterranean rooms exists among the cliff-dwellings in circular underground kivas, the variations of which are so well illustrated in Cliff Palace. In connection with these "pit rooms," which are never large, may be mentioned the large subterranean artificial excavations found scattered over the Pueblo area of the Southwest. Such occur in the Gila valley, and have been reported from the San Juan drainage; they have been identified as reservoirs and also as kivas. Some of these subterranean rooms are rightly identified as kivas, but others have architectural features that render this interpretation improbable. What their function was and how they are connected with the people who built the smaller subterranean rooms of the Southwest can be determined only by excavations and a study of the features of both types.