observations in the field but with the kind of linguistic research
above recorded. It would also apparently explain the occurrence of the
circular semisubterranean _kí wi tsi we_, or estufas. These being
sacred have retained the pristine form long after the adoption of a
modified type of structure for ordinary or secular purposes, according
to the well known law of survival in ceremonial appurtenances.

In a majority of the lava ruins (for example those occurring near
Prescott, Arizona), I have observed that the sloping sides rather than
the level tops of _mesa_ headlands have been chosen by the ancients as
building-sites. Here, the rude, square type of building prevails, not,
however, to the entire exclusion of the circular type, which, is
represented by loosely constructed walls, always on the _outskirts_ of
the main ruins. The rectangular rooms are, as a rule, built row above
row. Some of the houses in the upper rows give evidence of having
overlapped others below. (See section, Fig. 495.)


FLAT AND TERRACED ROOFS DEVELOPED FROM SLOPING MESA-SITES.

We cannot fail to take notice of the indications which this brings
before us.

(1) It is quite probable that the overlapping resulted from an
increase in the numbers of the ancient builders relative to available
area, this, as in the first instance, leading to a further massing
together of the houses. (2) It suggested the employment of rafters and
the formation of the _flat_ roof, as a means of supplying a level
entrance way and floor to rooms which, built above and to the rear of
a first line of houses, yet extended partially over the latter. (3)