The Yellowstone National Park has been set apart by Congress as a public reservation and pleasure-ground, and covers a surface of about fifty-five hundred square miles within the Rocky Mountains. Most of the Park is in the northwestern corner of Wyoming, but there are also small portions in Montana to the north and Idaho to the west. It is a tract more remarkable for natural curiosities than an equal area in any other part of the world, and within it are the sources of some of the greatest rivers of North America. The Yellowstone, Gardiner and Madison Rivers, which are the headwaters of the Missouri, flow out of the northern and western sides, while on the southern side originates the Snake River, one of the sources of the Columbia River of Oregon, and also the Green River, a branch of the Colorado, flowing into the Gulf of California. The central portion of the Park is a broad volcanic plateau, elevated, on an average, eight thousand feet above the sea, and surrounded by mountain ridges and peaks, rising to nearly twelve thousand feet, and covered with snow. The air is pure and bracing, little rain falls, and the whole district gives evidence of remarkable volcanic activity at a comparatively late geological epoch. It contains the most elevated lake in the world, Yellowstone Lake. The Yellowstone River flows into this lake, and then northward through a magnificent canyon out of the Park. Its most remarkable tributary within the Park is Tower Creek, flowing through a narrow and gloomy pass for two miles, called the Devil's Den, and just before reaching the Yellowstone having a fall of one hundred and fifty-six feet, which is surrounded by columns of breccia resembling towers. There is frost in the Park every month in the year, owing to the peculiar atmospheric conditions. The traces of recent volcanic activity are seen in the geysers, craters and terrace constructions, boiling springs, deep canyons, petrified trees, obsidian cliffs, sulphur deposits and similar formations. These geysers and springs surpass in number and magnitude those of the rest of the world. There are some five thousand hot springs, depositing mainly lime and silica, and over a hundred large geysers, many of them throwing water columns to heights of from fifty to two hundred and fifty feet. The most elaborate colors and ornamentation are formed by the deposits of the springs and geysers, these curiosities being mainly in and near the valleys of the Madison and Gardiner Rivers. An attempt has been made under Government auspices to have in the Park a huge game preserve, and within its recesses large numbers of wild animals are sheltered, including deer, elk, bears, big-horn sheep, and the last herd of buffalo in the country. Troops of cavalry and other Government forces patrol and govern the Park. THE MAMMOTH HOT SPRINGS.