r chief means of support. As irrigation was not known until long afterwards, arable areas were limited, hence they were compelled to divide into families or small clans, each occupying a single house. The traces of these solitary farm-houses show that they were at first single-storied. The name of an upper room indicates how the idea of the second or third story was developed, as it is _ósh ten u thlan_, from _ósh ten_, a shallow cave, or rock-shelter, and _ú thla nai e_, placed around, embracing, inclusive of. This goes to show that it was not until after the building of the first small farm-houses (which gave the name to houses) that the caves or rock-shelters of the cliffs were occupied. If predatory border-tribes, tempted by the food-stores of the horticultural farm-house builders, made incursions on the latter, they would find them, scattered as they were, an easy prey.
ADDED STORIES FOR CLIFF DWELLINGS DEVELOPED FROM LIMITATIONS OF CLIFF-HOUSE SITES.
[Illustration: FIG. 498.--A typical cliff-dwel