"Well," I said, "this is indeed a novel ride; for once in my life I have sidetracked the President of the United States! I am given the right of way over all." On we tore, along the smooth, hard road, and did not slacken our pace till, at the end of a mile or two, we began to mount the hill toward Fort Yellowstone. And not till we reached the fort did I learn that our mules had run away. They had been excited beyond control by the presidential cavalcade, and the driver, finding he could not hold them, had aimed only to keep them in the road, and we very soon had the road all to ourselves. Fort Yellowstone is at Mammoth Hot Springs, where one gets his first view of the characteristic scenery of the Park,--huge, boiling springs with their columns of vapor, and the first characteristic odors which suggest the traditional infernal regions quite as much as the boiling and steaming water does. One also gets a taste of a much more rarefied air than he has been used to, and finds himself panting for breath on a very slight exertion. The Mammoth Hot Springs have built themselves up an enormous mound that stands there above the village on the side of the mountain, terraced and scalloped and fluted, and suggesting some vitreous formation, or rare carving of enormous, many-colored precious stones. It looks quite unearthly, and, though the devil's frying pan, and ink pot, and the Stygian caves are not far off, the suggestion is of something celestial rather than of the nether regions,--a vision of jasper walls, and of amethyst battlements. With Captain Chittenden I climbed to the top, stepping over the rills and creeks of steaming hot water, and looked at the marvelously clear, cerulean, but boiling, pools on the summit. The water seemed as unearthly in its beauty and purity as the gigantic sculpturing that held it. The Stygian caves are still farther up the mountain,--little pockets in the rocks, or well-holes in the ground at your feet, filled with deadly carbon dioxide. We saw birds' feathers and quills in all of them. The birds hop into them, probably in quest of food or seeking shelter, and they never come out. We saw the body of a martin on the bank of one hole. Into one we sank a lighted torch, and it was extinguished as quickly as if we had dropped it into water. Each cave or niche is a death valley on a small scale. Near by we came upon a steaming pool, or lakelet, of an acre or more in extent. A pair of mallard ducks were swimming about in one end of it,--the cool end. When we approached, they swam slowly over into the warmer water. As they progressed, the water got hotter and hotter, and the ducks' discomfort was evident. Presently they stopped, and turned towards us, half appealingly, as I thought. They could go no farther; would we please come no nearer? As I took another step or two, up they rose and disappeared over the hill. Had they gone to the extreme end of the pool, we could have had boiled mallard for dinner.