162 THE CLIFF RUINS OF CANYON DE CHELLY [etm ayy.16 
inclosing wall that came outside of it. It will be noticed that chink- 
ing, both with mud and with spalls, was extensively practiced and 
seems here to have been an essential part of the construction. In this 
example it could have no relation to the finish of the wall, for the wall 
was not finished. 
Much of the masonry in the canyon is of the type described, but 
examples differ widely in degree of finish and in material selected. 
Some of the walls appear very rough and even crude, so much so that 
they almost appear to be the first efforts of a people at an unknown 
art, but a closer inspection shows that even the rudest walls were 
erected with a knowledge of the principles which were followed in the 
best ones, and that the difference resulted only from the care or lack 
of care employed. The rudest walls are much superior to the masonry 
of the Navaho cists which are found in conjunction with them and which 
are constructed on a different method. 
Although walls were often built on sloping rock, and the builders 
had experience and at times disastrous experience to guide them, the 
necessity for a flat and solid foundation was never appreciated. Walls 
were sometimes built on loose débris; even refuse which had been coy- 
ered and formed an artificial soil was considered sufficient. There are 
many instances in the canyon where lack of foresight or lack of knowl- 
edge in this respect has brought about the destruction of walls. Walls 
resting on foreign material occur throughout the region; they are not 
confined to any one class of ruins or to any part of the canyon, but are 
found as much or more in the most recent as in the most ancient 
examples. Mummy Cave ruin and Casa Blanca are good examples. 
In the latter the small room on the left of the upper group (plate 
XLVil) is especially interesting. The side walls appear to rest on a 
deposit of refuse nearly 2 feet thick, which in turn rests on the sloping 
rock. The front wall is supported by a buttress as shown; without 
this support it would certainly have been pushed out. The buttress 
appears to have been built at the same time as the front wall, although 
its use in this way is not aboriginal. The whole arrangement is such 
as would result if this room, originally represented by a low front wall 
perhaps, were constructed when the site became inadequate and con- 
sequently at a late period in its occupancy. 
The character of the refuse and débris upon which some of the walls 
rest is worth notice. It is well known that sheep were introduced into 
this country by the Spaniards, and the presence in the ruins of sheep 
dung, or of a material which closely resembles it, is important. Much 
of this is due to subsequent Navaho occupancy, and many ruins are 
used today by these Indians as sheepfolds. It is said, moreover, that 
at the time of the Navaho war, when the soldiers bayoneted all the 
sheep they could find, large flocks were driven up into some cliff ruins 
that are almost inaccessible, and kept there for a time in security. 
But many instances are found where the walls rest directly upon layers 
