the construction of the parapets. These boulders were, on an average,
thirty-five inches long, twenty-five inches thick and fifteen inches
wide; while the stones used in the house walls measured, on the
average, fourteen by nine by seven inches.

On the western end of the ridge is a small house group, which, for
convenience sake, I will designate as "Mason's Ruins." They showed
a decidedly higher method of construction, and the walls were better
preserved, than in any we had seen so far. The ground plans could be
readily made out, except in a small part of the southwest corner. These
walls stood three to five feet high, and the stones here too were
dressed only by fracture. They were laid in gypsiferous clay, a mass
of which lay close to the southwest corner. This clay is very similar
to the material used by the Moquis in whitening their houses. The
stones themselves were felsite, which abounds in the locality. The
blocks have an average size of twelve inches square by six inches
thick. It should be noted that no regard was paid to the tying of the
corners and the partition walls; but considerable care had been taken
in making the walls vertical, and the angles were fairly true. The
walls were almost twelve inches thick, and on the inner side they
had evidently never been plastered.

Being coated with some white plaster, these ruins look white at a
distance, and the Mexicans therefore called them _casas blancas_. I
heard of an extensive group of such buildings near Sahuaripa, and
there are also some ruins of this category near Granados, and in
the hills east of Opoto. Undoubtedly they belong to a more recent
period than the rude stone structures described before. Most of the
ancient remains of the Sierra are remnants of tribes that expanded
here from the lowlands, and only in comparatively recent times have