[Illustration: Hot Springs and Castle Geyser. The spring in the foreground is in all respects the most beautiful one in the National Park. The ornamental rim is nearly circular, being about twenty-two feet. The depth is unknown. When the rays of the sun fall nearly vertically on the almost unnaturally transparent waters, all the colors of the prism are produced. The temperature is about 180°. Just in the background is the Castle Geyser, which is so called from the form of its crater. It is really an old ruin. It seldom plays, but when in operation it is a terrific power, shaking the ground for a considerable distance. It continues with great force for one to two hours.] [Illustration: Mammoth Hot Springs on Gardiner’s River. The peculiar character of the deposits is well shown in this picture. The larger hot springs are located on the terrace above, and, as the heated water flows over the declivity, the beautiful pool-like basins are formed from four to eight feet wide and two to four feet deep. As the water leaves the spring and flows over the sides of the mountain, it loses a portion of its heat, so that the bather may choose any temperature he may desire. These pools are sometimes called Diana’s Baths. The deposit is as white as snow.] [Illustration: Mammoth Hot Springs, Lower Basin. The four succeeding pictures represent the calcareous group. There are two kinds of hot springs in the park, called siliceous and calcareous from the character of their deposits. A large amount of lime is held in solution in the hot water which is precipitated in wonderfully unique architectural forms on the steep sides of the mountains, as shown in the photograph. These springs are located in the valley of the Yellowstone, near the northern boundary of the park, and are named White Mountain Hot Springs on the map. At the present time they are most accessible by the way of Fort Ellis, Montana, and the Yellowstone Valley.] [Illustration: Cap of Liberty Mammoth Hot Springs. This is a fine example of an extinct geyser or fountain spring. It doubtless operates much like one of our artificial fountains, throwing up a column of water several feet, by a succession of impulses, building up a cone by overlapping layers of lime, like the thatch on the roof. The cone is forty-two feet high and about twenty-five feet in diameter at its base. When the hydrostatic force begins to abate, the cone is gradually closed up at the summit, as is shown in the photograph. These dead springs or geysers are a common feature in the park, and are called, in the language of Iceland a “laug.” It is only a calcareous spring that can form so curious and lofty a cone as this.] [Illustration: Lower Falls of the Yellowstone. A more distant view of the falls. The photograph however, conveys but a dim conception of the ruggedness of the surroundings.]