Detailed Description.

The Casa Grande ruin is often referred to as an adobe structure.  Adobe construction, if we limit the word to its proper meaning, consists of the use of molded brick, dried in the sun but not baked.  Adobe, as thus defined, is very largely used throughout the southwest, more than nine out of ten houses erected by the Mexican population and many of those erected by the Pueblo Indians being so constructed; but, in the experience of the writer, it is never found in the older ruins, although seen to a limited extent in ruins known to belong to a period subsequent to the Spanish conquest.  Its discovery, therefore, in the Casa Grande would be important; but no trace of it can be found.  The walls are composed of huge blocks of earth, 3 to 5 feet long, 2 feet high, and 3 to 4 feet thick.  These blocks were not molded and placed in situ, but were manufactured in place.  The method adopted was probably the erection of a framework of canes or light poles, woven with reeds or grass, forming two parallel surfaces or planes, some 3 or 4 feet apart and about 5 feet long.  Into this open box or trough was rammed clayey earth obtained from the immediate vicinity and mixed with water to a heavy paste.  When the mass was sufficiently dry, the framework was moved along the wall and the operation repeated.  This is the typical pise or rammed-earth construction, and in the hands of skilled workmen it suffices for the construction of quite elaborate buildings.  As here used, however, the appliances were rude and the workmen unskilled.  An inspection of the illustrations herewith, especially of plate LV, showing the western wall of the ruin, will indicate clearly how this work was done.  The horizontal lines, marking what may be called courses, are very well defined, and, while the vertical joints are not apparent in the illustration, a close inspection of the wall itself shows them.  It will be noticed that the builders were unable to keep straight courses, and that occasional thin courses were put in to bring the wall up to a general level.  This is even more noticeable in other parts of the ruin.  It is probable that as the walls rose the exterior surface was smoothed with the hand or with some suitable implement, but it was not carefully finished like the interior, nor was it treated like the latter with a specially prepared material.  The material employed for the walls was admirably suited for the purpose, being when dry almost as hard as sandstone and practically indestructible.  The manner in which such walls disintegrate under atmospheric influences has already been set forth in detail in this report.  An inhabited structure with walls like these would last indefinitely, provided occupancy continued and a few slight repairs, which would accompany occupancy, were made at the conclusion of each rainy season.  When abandoned, however, sapping at the ground level would commence, and would in time level all the walls; yet in the two centuries