Some of these furnish a clew to the manner in which the dwellings were formed by scraping and burrowing.

Splinters of obsidian and of basalt--sharp fragments, resembling clumsy chisels or knives--served to dig an oblong hole in the soft pumice or tufa of the cliff.

After this narrow cavity had penetrated a depth of one or two feet, the artisan began to enlarge it inside, until a room was formed for which the tunnelled entrance served as a doorway.

The room, or cell, was gradually finished in a quadrangular or polygonal shape, with a ceiling high enough to permit a person of average size to stand erect.

Not unfrequently side rooms were excavated connecting with the first by low apertures, to pass through which it was necessary to stoop, or even to creep on all fours.