Bartlett in 1851, while acting as United States Commissioner, in fixing the United States and Mexican boundary line. The Casas Grandes, according to Mr. Bartlett, are built of adobe or mud, in large quadrangular blocks measuring about twenty-two inches in thickness by three feet or more in length. The irregularity of the length of the blocks, however, seemed to indicate that they had been formed on the wall, _in situ_, by means of a box open at the ends, which, when the block dried, was moved along to mould a fresh block. The mud is filled with coarse gravel from the plateau, which gives greater hardness to the material. The Casas face the cardinal points and consist of erect and fallen walls, ranging from five to thirty feet in height. The accumulation of rubbish is, however, considerable, and if the highest standing walls rest upon a common level with the lowest, they will measure from forty to fifty feet in height. The edifice was discovered in ruins by the conquerors, and could not have been occupied for a century, at the least calculation, prior to its discovery. It is, therefore, reasonable to presume that all the walls now standing were originally much higher than at present. It appears that the outer portions of the edifices were the lowest, and not more than one story in height, while the central ones were from three to six stories. The central or inner walls are better preserved, partly by their greater thickness—five feet at the base—and partly by the heaps of ruined walls which have fallen around them. Once prostrate, the blocks absorb the water, and in a few years are reduced to a mass of mud and gravel. It was with difficulty that Mr. Bartlett traced all the outlines of the buildings; but close examination revealed the fact that three lofty edifices were connected into one by means of a low range of buildings, one storey high, which may have merely inclosed intervening courts. The total length of this continuous edifice was at least 800 feet by 250 feet wide. A regular and continuous wall was observed on the south side, while the eastern and western fronts, with their projecting walls, were very irregular. The question of the exact number of stories is not capable of solution, as no vestige of timbers or wood now remains. The explorer could not even detect a trace of any cavities where the floor-timbers had been inserted in the walls, so decayed and washed was their condition. Many doorways remained, but the lintels having decayed, the tops had fallen in. Clavigero states that the edifice had “three floors with a terrace above them and without any entrance to the under floor, so that a scaling ladder is necessary.” García Condé confirms this statement as to the three stories besides a roof,[441] while both authors consider this to have been a station on the Aztec migration. Certainly, no architectural analogies with the remains farther south justify this opinion. Mr.