All the strata composing this formation are very soft; the purple-gray material of the middle layer is so soft that its surface can be rubbed off with the hand. They are also minutely stratified or laminated, and the laminæ are not well cemented together, so that a blow on the roof of a cavity with a stone or other implement will bring off slabs varying from half an inch to an inch and a half in thickness. These thin strata or laminæ are of unequal hardness, weathering in places several inches into the face of the rock in thin streaks of a few inches or less. The middle purple stratum exhibits this quality somewhat more decidedly than the others, and this fact has doubtless determined the selection of this stratum for the location of the lodges, as a room can be excavated in it more easily than a room of a similar size could be built up with loose rock. The almost absolute dependence of the native builder on nature as he found it is well illustrated by these cavate lodges. At a point in the northern wall of the northernmost canyon, shown in the diagram (figure 289) and in plate XXVI, there is a small fault with a throw of about 2½ feet, and the floors of the lodges west of the fault are just that much lower than the floors east of it. Furthermore, where the purple-gray stratum in which the lodges occur is covered up by the rising ground surface, the cavate lodges abruptly cease. In the northern and southern ends of the group the talus encroaches on and partly covers the purple-gray stratum, and in these places the talus has been removed from the face of the rock to permit the excavation of lodges. In short, the occurrence of the cavate lodges in this locality is determined absolutely by the occurrence of one particular stratum, and when that stratum disappears the lodges disappear. So far as can be ascertained without actually excavating a room there is no apparent difference between the stratum in which the lodges occur and the other purple strata above and below it. That there is some difference is indicated by the confinement of the lodges to that particular level, but that the difference is very slight is shown by the occurrence in two places of lodges just above the principal tier, a kind of second-story lodge, as it were. It is such differences in environment as these, however, often so slight as to be readily overlooked, which determine some of the largest operations carried on by the native builders, even to the building of some of the great many-storied pueblos, and, stranger still, sometimes leading to their complete abandonment. In the region under discussion cavate lodges usually occur in connection with and subordinate to village ruins, and range in number from two or three rooms to clusters of considerable size. Here, however, the cavate lodge is the feature which has been most developed, and it is noteworthy that the village ruins that occur in connection with them are small and unimportant and occupy a subordinate position.