Plate LX shows walls in which an abundance of mud mortar was used, and the effect is that of a plastered wall. The difference between these walls and those shown in plate LVII is only one of degree, the wall shown in plate LIX being of an intermediate type. No instance occurs in the canyon where a coating of mud was evenly applied to the whole surface of a wall, in the way, for example, that stucco is used by us. It seems probable, therefore, that the application of plaster as a finish grew out of the use of stone spalls for chinking, and its prevalence in modern as compared with old structures is suggestive. It is not claimed, however, that because we have examples of the intermediate stages in De Chelly that the process was developed there. The step is such a slight one that it might have been made in a hundred different localities at a hundred different times or at one time; but it is well to note that in any given group of ruins or locality it is likely to be later than masonry chinked with stones. Surface finishing in mud plaster is the prevailing method at the present day, and well-executed masonry of stone carefully chinked is almost invariably ancient. The use of surface plaster is largely responsible for the deterioration of stonework that has taken place since the beginning of the historic period. The modern village of Zuni, which dates from the beginning of the eighteenth century, although built on the site of an older village, is essentially a stone-built village, though that fact would never appear from a cursory examination, so completely is the stonework covered by surface plaster. In Tusayan (Moki) walls have been observed in progress of erection. The stones were laid up dry, and some time after, when the rains came and pools of water stood here and there in pockets on the mesa top, mud mortar was mixed and the interstices were filled. This method saved the transportation of water from the wells below up to the top of the mesa, a task entailing much labor. Doubtless a similar method was followed in De Chelly, where the stream bed carries water only during a part of the year. But stone was also actually laid in mud mortar, as shown in plate LII, which illustrates a rough type of masonry. It is probable that the practice of chinking grew up out of the scarcity of water, when walls were erected during the dry season and finished when the rains made the manufacture of mud mortar less of a task. The rough wall shown in the illustration is the outside of an interior wall of a kiva, and it was probably covered by the rectangular inclosing wall that came outside of it. It will be noticed that chinking, 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.