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.

One of the most surprising features of the Grand canon is its cleanness—­its freedom from debris.  It is a home of the gods, swept and garnished; no litter or confusion or fragments of fallen and broken rocky walls anywhere.  Those vast sloping taluses are as clean as a meadow; rarely at the foot of the huge vertical walls do you see a fragment of fallen rock.  It is as if the processes of erosion and degradation were as gentle as the dews and the snows, and carved out this mighty abyss grain by grain, which has probably been the case.  That much of this red sandstone, from the amount of iron it contains, or from some other cause, disintegrates easily and rapidly, is very obvious.  Looking down from Hopi Point upon a vast ridge called the “Man-of-War,” one sees on the top, where once there must have been a huge wall of rock, a long level area of red soil that suggests a garden, the more so because it is regularly divided up into sections by straight lines of huge stone placed as if by the hands of man.

One’s sense of the depths of the canyon is so great that it almost makes one dizzy to see the little birds fly out over it, or plunge down into it.  One seems to fear that they too will get dizzy and fall to the bottom.  We watched a line of tourists on mules creeping along the trail across the inner plateau, and the unaided eye had trouble to hold them; they looked like little red ants.  The eye has more difficulty in estimating sizes and distances beneath it than when they are above or on a level with it, because it is so much less familiar with depth than with height or lateral dimensions.