670 THU POPULAR SCIENCE MONTHLY. 



of the Mancos. Here there are two towers on the very edge of the 

 mesa, so close that the outer walls are not complete, but are open to- 

 ward the cliff. In the smaller of these towers, the outer wall is twenty- 

 two feet in diameter, the inner twelve feet. In the larger tower, the 

 diameters of the walls are respectively one hundred and forty and one 

 hundred and twenty-three feet. Both are much broken down, so that 

 the original height can not be estimated. In the face of the cliff, 

 directly beneath these towers, are several cave-dwellings connected 

 with the top of the cliff by steps cut in its face. 



In the caiion of the Mancos, on the river-bottom, are the ruins of a 

 large tower, the diameters of whose walls are respectively forty-three 

 and twenty-five feet. 



On a low bench near the McElms, a dry canon which heads in the 

 plateau, and enters the San Juan below the mouth of the Mancos, is a 

 large settlement. On one side of the town is a large tower, remark- 

 able as having triple walls, whose diameters are respectively forty-five, 

 thirty-five, and fifteen feet. The space between the outer and middle 

 walls is divided by partition-walls, while that between the middle and 

 inner walls is not. In this and all other such structures there are no 

 openings through the walls into the interior apartment. Access to it 

 was had probably through a subterranean passage, as has been observed 

 in at least one case. 



Connected with the agricultural and mesa towns are, in many cases, 

 watch-towers usually of circular form, perched on fragments of rocks 

 in commanding positions, whence the approach of enemies can be de- 

 tected. These are small and with single walls. In the neighborhood 

 of some agricultural settlements are holes dug in the earth, and the 

 earth thrown up in heaps in front, as in rifle-pits. They probably 

 were made for a similar use. 



The rocks of which the cafion cliffs are composed are of sandstone 

 and shale. The former is hard and is acted on by the elements slowly, 

 while the latter is easily disintegrated. Hence it is common to find 

 that strata pathways up the cliff have disintegrated faster than those 

 above and below, leaving horizontal crevices of greater or less height 

 and depth. These crevices have been utilized by these people, when 

 hard pressed by their enemies, as strongholds. They built walls across 

 the whole fronts, leaving only little holes for egress and ingress, light 

 and air. Thus walled in, their position was absolutely impregnable 

 from above or below. It is astonishing in what a limited space these 

 beings contrived to exist ; some of these cave-dwellings are scarcely 

 large enough for a man to crawl into. 



More pretentious than these are the cliff -houses, which are built in 

 similar situations, differing only in the height of the crevices. Many 

 excellent examples of these have been found. They are generally well 

 preserved, as their situations protect them in great measure from the 

 elements. There are several in the canon of the Rio Mancos. In one 



