The Spell of the Rockies by Enos A. Mills

During my first boyish exploring trip in the Rocky Mountains I was impressed with the stupendous changes which the upper slope of these mountains had undergone. In places were immense embankments and wild deltas of debris that plainly had come from elsewhere. In other places the rough edges of the canyons and ridges had been trimmed and polished; their cliffs and projections were gone and their surfaces had been swept clean of all loose material. Later, I tried vainly to account for some canyon walls being trimmed and polished at the bottom while their upper parts were jagged. In most canyons the height of the polishings above the bottom was equal on both walls, with the upper edge of the polish even or level for the entire length of the canyon. In one canyon, in both floor and walls, were deep lateral scratches in the rocks.

One day I found some polished boulders perched like driftwood on the top of a polished rock dome; they were porphyry, while the dome was flawless granite. They plainly had come from somewhere else. How they managed to be where they were was too much for me. Mountain floods were terrible but not wild enough in their fiercest rushes to do this. Upon a mountainside across a gorge about two miles distant, and a thousand feet above the perched boulders on the dome, I found a porphyry outcrop; but this situation only added to my confusion. I did not then know of the glacial period, or the actions of glaciers. It was a delightful revelation when John Muir told me of these wonders.