Moving down the stream on the north side, past springs and small geysers of every variety, for a distance of three miles, we then traversed a valley five miles in length, swampy in many places, and in others much obstructed by fallen timber. Thermal springs were scattered along the whole route, but none large enough to be remarkable here. In eight miles we came to an enormous bluestone spring, nearly circular in form, 450 yards in circumference, and of unfathomable depth, boiling hot, and with clouds of steam evolving from its surface. It has built up a hill 50 feet above the general level, and covering about 100 acres with a calcareous bed. The margin of the great basin is bounded by a rim 30 feet back from the brink of the crater, and elevated a few inches. The waters overflow in every direction, keeping the long slopes constantly wet. The deposits are of variegated colors -- a circumstance not before remarked in any springs of this class; the water boils up slightly in many places far out in the basin, but steadily, and with no indication of violent or periodic action. The steam rising is evolved from the surface of the water, and does not escape through it from beneath. The margin of this lake is a hundred and fifty yards from the river, which has cut away its deposit to a bluff bank, 46 feet in height, at that distance. Between this bluff and the basin, but at a lower level, by 20 feet, is a geyser with a basin 50 feet in diameter, and playing a strong jet from the center to the height of 20 feet. Just beyond this, and at a different level still, are several smaller geysers, and a bluestone spring 70 feet in diameter. Flowing from these latter over the bank into the river are five streams of boiling water, either one large enough to run an ordinary grist mill. These steaming cataracts are among the most beautiful we have witnessed on the trip. Below the Great Basin, and at a distance from the bank, are two more bluestone springs, respectively 75 and 100 feet in diameter. These do not flow. Here the valley opens out to several miles in width, being of triangular shape, and about twelve miles in length. The Madison River comes in from the south, along the west side of this valley, joining the Firehole River at its northwest angle. In this large valley has formerly been a repetition of Firehole Basin, but on a much larger scale. On the south side are two hills of calcareous deposit, having gigantic but extinct craters on their summits. These hills are for the most part bare on the slopes, but are in some places grown up with pine timber, and are 800 feet in height. Some of the fragments of the crater walls are 50 feet in altitude. The south side, between the forks of the rivers, contains innumerable extinct craters of great size, and a few small ones, in operation, but with a low grade of action. On the north side of the Firehole River the valley slopes gradually from the bluffs to the river, a space of three miles in width, and is a calcareous swamp, with the summits of extinct craters projecting by hundreds above its surface. This great marsh has been deposited by waters from a vast series of geysers and springs along the foot-hill range; though much decreased in action many of these are still in operation, and for miles the swamp is yet flooded with their waters. These we passed at a distance, and without visiting, but saw their clear fountains and steam jets playing on the side hill, as we threaded the swamp.  The amount of water flowing down from this system is enormous, and it was with the utmost difficulty that we found a passage through the slimy morass. Along the banks of the Firehole River were seen numerous steam jets, and in the center of the valley is  Go to next page