same principle. Evidently these walls were built for the protection
of the people in time of war.

About five miles south of our camping place the river turns eastward,
and again two miles below this point it receives a tributary from
the west. One day I followed the broken cordon on its eastern bank,
then turned north and ascended an isolated mountain, which rises
about fifteen hundred feet high above the river. There is a small
level space on top, and on this there has been built, at some time,
a fortress with walls of undressed stones from two to six feet high
and three feet thick. It was about fifty paces long in one direction,
and about half that length in the other. Remains of houses could be
traced, and inside of the walls themselves the ground plan of three
little chambers could be made out.

On the Bavispe River we photographed a trinchera which was about eight
feet high and thirty feet long; and one of the foremen observed one
which was at least fifteen feet high.

I decided to move the camp one and a half miles down the river, and to
its right bank, on a cordon, where Mason, one of my Mexican foremen,
had discovered some ruins. It was very pleasant here after the rather
cool bottom of the valley, which in the morning was generally covered
with a heavy fog. On this ridge were many traces of former occupancy,
parapet walls and rude houses divided into small compartments. The
parapets were lying along the north and south faces of the houses,
and just on the brink of the narrow ridge. On the south side the ridge
was precipitous, but toward the north it ran out in a gentle shallow
slope toward the next higher hill. The building material here is a
close-grained felsite, and huge fragments of it have been used in