It is quite worth while to go down into the canon on mule-back, if only to fall in love with a mule, and to learn what a sure-footed, careful, and docile creature, when he is on his good behavior, a mule can be. My mule was named "Johnny," and there was soon a good understanding between us. I quickly learned to turn the whole problem of that perilous descent over to him. He knew how to take the sharp turns and narrow shelves of that steep zigzag much better than I did. I do not fancy that the thought of my safety was "Johnny's" guiding star; his solicitude struck nearer home than that. There was much ice and snow on the upper part of the trail, and only those slender little legs of "Johnny's" stood between me and a tumble of two or three thousand feet. How cautiously he felt his way with his round little feet, as, with lowered head, he seemed to be scanning the trail critically! Only when he swung around the sharp elbows of the trail did his forefeet come near the edge of the brink. Only once or twice at such times, as we hung for a breath above the terrible incline, did I feel a slight shudder. One of my companions, who had never before been upon an animal's back, so fell in love with her "Sandy" that she longed for a trunk big enough in which to take him home with her. It was more than worth while to make the descent to traverse that Cambrian plateau, which from the rim is seen to flow out from the base of the enormous cliffs to the brink of the inner chasm, looking like some soft, lavender-colored carpet or rug. I had never seen the Cambrian rocks, the lowest of the stratified formations, nor set my foot upon Cambrian soil. Hence a new experience was promised me. Rocky layers probably two or three miles thick had been worn away from the old Cambrian foundations, and when I looked down upon that gently undulating plateau, the thought of the eternity of time which it represented tended quite as much to make me dizzy as did the drop of nearly four thousand feet. We found it gravelly and desert-like, covered with cacti, low sagebrush, and other growths. The dim trail led us to its edge, where we could look down into the twelve-hundred-foot V-shaped gash which the river had cut into the dark, crude-looking Archaean rock. How distinctly it looked like a new day in creation where the horizontal, yellowish-gray beds of the Cambrian were laid down upon the dark, amorphous, and twisted older granite! How carefully the level strata had been fitted to the shapeless mass beneath it! It all looked like the work of a master mason; apparently you could put the point of your knife where one ended and the other began. The older rock suggested chaos and turmoil; the other suggested order and plan, as if the builder had said, "Now upon this foundation we will build our house." It is an interesting fact, the full geologic significance of which I suppose I do not appreciate, that the different formations are usually