a circle, and lay out the four sides of a quadrangular structure with tolerable correctness. It is not too much to assume that with a string and sinker attached the Village Indian had the plumb-line, and could prove his wall as well as we can. At all events, the eye still proves the general correctness of their work.
The adobe mortar of the Pueblo Indians is something more than mud mortar, although far below a mortar of lime and sand. Adobe is a kind of finely pulverized clay with a bond of considerable strength by mechanical cohesion. In Southern Colorado, in Arizona, and New Mexico, there are immense tracts covered with what is called adobe soil. It varies somewhat in the degree of its excellence. The kind of which they make their pottery has the largest per cent, of alumina, and its presence is indicated by the salt weed which grows in this particular soil. This kind also makes the best adobe mortar. The Indians use it freely in laying their walls, as freely as our masons use lime mortar; and although it never acquires the hardness of cement, it disintegrates slowly. The mortar in these walls is still sound, so that it requires some effort of strength to loosen a stone from the wall and remove it. But this adobe mortar is adapted only to the dry climate of Southern Colorado, Arizona, and New Mexico, where the precipitation is less than five inches per annum. The rains and frosts of a northern climate would speedily destroy it. To the presence of this adobe soil, found in such abundance in the regions named, and to the sandstone of the bluffs, where masses are often found in fragments, we must attribute the great progress made by these Indians in house-building.
The exclusive presence of this adobe mortar in all New Mexican structures of the aboriginal period shows that the tribes of New Mexico were then ignorant of a mortar of lime and sand. And here a digression may be allowed to consider whether a cement of this grade was known to the aborigines. Theoretically, the use of a mortar composed of quick-lime and sand, which gives a cement chemically united, would not be expected of the Indian tribes either in North or South America. There is no sufficient proof that they ever produced a cement of this high grade. It requires a kiln, artificially constructed, and a concentrated heat to burn limestone into lime, supposing they had learned that lime could be thus obtained, and some
