There is probably another explanation of what we see here.  Apart from the mechanical weathering of the rocks as a result of the arid climate, wherein rapid and often extreme changes of temperature take place, causing the surface of the rocks to flake or scale off, there has doubtless been unusual chemical weathering, and this has been largely brought about by the element of iron that all these rocks possess.  Their many brilliant colors are imparted to them by the various compounds of iron which enter into their composition.  And iron, though the symbol of hardness and strength, is an element of weakness in rocks, as it causes them to oxidize or disintegrate more rapidly.  In the marble canon, where apparently the rock contains no iron, the lateral erosion has been very little, though the river has cut a trench as deep as it has in other parts of its course.

How often I thought during those days at the canon of the geology of my native hills amid the Catskills, which show the effects of denudation as much older than that shown here as this is older than the washout in the road by this morning’s shower!  The old red sandstone in which I hoed corn as a farm-boy dates back to Middle Palaeozoic time, or to the spring of the great geologic year, while the canon is of the late autumn.  Could my native hills have replied to my mute questionings, they would have said:  “We were old, old, and had passed through the canon stage long before the Grand Canon was born.  We have had all that experience, and have forgotten it ages ago.  No vestiges of our canons remain.  They have all been worn down and obliterated by the strokes of a hand as gentle as that of a passing cloud.  Where they were, are now broad, fertile valleys, with rounded knolls and gentle slopes, and the sound of peaceful husbandry.  The great ice sheet rubbed us and ploughed us, but our contours were gentle and rounded aeons before that event.  When the Grand Canon is as old as we are, all its superb architectural features will have long since disappeared, its gigantic walls will have crumbled, and rolling plains and gentle valleys will have taken its place.”  All of which seems quite probable.  With time enough, the gentle forces of air and water will surely change the whole aspect of this tremendous chasm.

On the second day we made the descent into the canon on mule-back.  There is always satisfaction in going to the bottom of things.  Then we wanted to get on more intimate terms with the great abyss, to wrestle with it, if need be, and to feel its power, as well as to behold it.  It is not best always to dwell upon the rim of things or to look down upon them from afar.  The summits are good, but the valleys have their charm, also; even the valley of humiliation has its lessons.  At any rate, four of us were unanimous in our desire to sound that vast profound on mule-back, trusting that the return trip would satisfy our “climbing” aspirations, as it did.