MORGAN. ] ADOBE MORTAR. 17 
a circle, and lay out the four sides of a quadrangular structure with tolera- 
ble 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 wellas wecan. 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 abuudance 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 struc- 
tures 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 
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