There are ruins scattered all over the South-west, many of which were built by the same set of Amerinds, and do not represent a vanished population. Still, I believe that the population was at one time much greater than it was when our acquaintance with it began. Internecine wars resulting from a diminution of water-supply; diseases introduced by the whites; and also the attacks and absorption of tribes by the wilder Amerinds, being some of the causes of the diminution. It would not be possible to describe even all the prominent ruins here, but I will mention several. Beginning easterly of the Rio Grande, we find the Pecos Ruins first of importance. There are also remains of a large adobe Catholic church and a convent here, not finally and fully abandoned till about 1840. The ruins consist of two chief buildings on a low table, surrounded by an artificial wall. The buildings were in the form of rectangles, with courts within, one 55 by 440 feet, and the other 170 by 350 feet. In places, they were three or four stories high, terraced, Pueblo fashion. The construction was slightly different from the ordinary, as the upper floor and roof beams rested mainly on heavy upright posts set into the walls, and not directly on the walls themselves. The whole framework was thus independent of the enclosing walls, very much as our modern steel frame buildings are. The walls were of sandstone slabs, and were from one to two feet thick. Another group of important ruins, and about the finest specimens of the stone buildings of the ancient Pueblos, is that of the Chaco, in north-western New Mexico.[202] There are eleven chief ruins, and many smaller ones. The principal ruins were once houses three, four, or perhaps five stories high, all built of sandstone slabs and blocks obtained from the débris of the cliffs. Some of the walls are still standing to the height of thirty or forty feet. All are not uniform in the way the stones are laid, the variation being due to building at different times, and to a variation of the available supply of slabs. The stones were usually laid so closely, and so carefully chinked with spalls, that the outside of the walls resembles a smooth mosaic; though adobe mortar and rubble were freely used in the interior. Lintels, as was generally the case throughout America, were of wood. The date of the abandonment of these buildings is not known. They were first mentioned by Gregg, in 1844.[203] [Illustration: THEORETIC ROOF CONSTRUCTION OF MITLA W. H. Holmes ] [Illustration: CEILING OR ROOF PLAN GROUND PLAN OF A KIVA AND CEILING PLAN OF ANOTHER