On the next page is the ground plan of the Temple of Isis, about twenty-five hundred feet high. The first story is about a thousand feet; the second, three hundred and fifty feet; the third, one hundred and fifty feet; the fourth, five hundred feet; and the fifth, five hundred feet. The finish at the top shows as a heavy crumbling wall, probably one hundred feet or more high. How the mass seems to be resisting the siege of time, throwing out its salients here and there, and meeting the onset of the foes like a military engineer. The pyramidal form of these rock-masses is accounted for by the fact that they were carved out from the top downward, and that each successive story is vastly older than the one immediately beneath it. The erosive forces have been working whole geologic ages longer on the top layer of rock than on the bottom layer; hence the topmost ones are entirely gone or else reduced to small dimensions. But what feature or quality of the rock it is that lends itself so readily or so inevitably to these architectural forms--the four square foundations, the end pilasters and balustrades, and so on--is to me not so clear. The peculiar rectangular jointings, the alternation of soft and hard layers, the nearly horizontal strata, and other things, no doubt, enter into the problem. Many of these features are found in our older geology of the East, as in the Catskills --horizontal strata, hard and soft layers alternating, but with the vertical jointing less pronounced; hence the Catskills have few canon-like valleys, though there are here and there huge gashes through the mountains that give a canon effect, and there are gigantic walls high up on the face of some of the mountains that suggest one side of a mighty canon. In the climate of the Catskills the rock-masses of the Colorado would crumble much more rapidly than they do here. The lines of many of these natural temples or fortresses are still more lengthened and attenuated than those of the Temple of Isis, appearing like mere skeletons of their former selves. The forms that weather out the formation above this, the Permian, appear to be more rotund, and tend more to domes and rounded hills.