As the coil proceeded, thick coats of plaster were laid on inside and outside.

This plaster, which is the same material as that of which the houses are constructed, got thoroughly mixed with the straw during the process of building, and the entire structure was finished without any opening except the one at the top.

The other apertures were undoubtedly cut out afterward.

There is no trace of withes or other binding material to hold the straw cables in place.

They are kept in position only by the plaster, which here, as in the houses, is almost as hard as the conglomerate of the surrounding rocks.
My Mexicans from Sonora called it _olla_, a jar, and insisted that it was a vessel used for keeping water; but this is entirely improbable, for several reasons, mainly because the river is in close proximity and easy of access.