YELLOWSTONE LAKE AND CA:RON. The Yellow stone River enters the park at its southeastern corner in a marshy valley, and soon flows into the southeastern arm of Yellowstone Lake. The lake lies at an altitude of 7741 feet above sea level, being the hugest lake at that altitude in North America, and one of the most beautiful mountain lakes in the world. It•is 20 miles long and 10 miles wide, but of a shape so irregular that it has a shore line of over 100 having sev eral finger-like arms extending west and south ward. Its shores are densely forested, and on the east towers a group of numerous lofty peaks in cluding the highest within the park. Ancient beaches indicate that the lake was formerly much larger and deeper than now, and that instead of discharging into the Yellowstone River and the Atlantic Ocean. it formerly sent its waters to the Pacific Ocean. After leaving the lake at the northern end the river is broad and tranquil for several miles. Then it becomes narrow, rapid, and broken by huge rocks, and, after turning to the northeast, it falls over a precipice 110 feet high, and is narrowed to a width of 100 feet. A half mile below this cataract, which is known as the Upper Falls, the river plunges again over a ledge of trachyte, and falls 310 feet into the Grand Callon. Here it rushes for 20 miles as an emerald green and foaming stream shut in by precipitous or exceedingly steep walls of lava 1200 to 1500 feet high, which are brightly col ored with red, yellow, and green incrustations, and crowned by dark green spruces above. Turn ing again to the northwest, the river passes through another canon whose walls are lower and less definite, and then emerges from the park.
lloT AND GEYSERS. Springs of all kinds abound throughout the park. There are countless springs of cold pure water and some cold mineral springs, but the peculiar feature which has especially made the park famous are the hot springs due to the volcanic heat still present beneath the surface. There are hot springs everywhere, in the valleys and on the mountain summits, on the plateaus and at the bottoms and on the sides of the cafions, and even at the bottoms of the rivers and lakes. They range iu size from a few square inches to several acres, and most of them are highly charged with mineral matter, mostly siliceous, while many emit sulphurous fumes, and some are distinctly poisonous. The ground for many acres around the principal hot springs and geyser regions is covered with white incrustations of silica or calcareous minerals, often streaked with bright coloring matter, and the larger springs have built up small cones of these materials. Of the
non-eruptive springs the most famous are the Mammoth Hot Springs, situated near the north ern entrance to the park. They are charged with calcareous matter derived from the Cretaceous limestone beneath the lava, and have deposited this material in a dazzling white cone several hundred feet high and consisting of semicircular basins arranged in terraces on the hill slope. The basins are one to eight feet in diameter and one to two feet deep, and their walls are beauti fully scalloped, ornamented with natural bead work, and streaked with bright red and yellow. The water issues at a boiling temperature in the large basin at the summit, and cools gradually as it de,cends into the successive basins below. There are several extinct basin cones in the neighborhood covered with humus and vegeta tion. such as Terrace Mountain, which is much larger than the present :Mammoth Springs.
There are at least seventy eruptive hot springs or geysers in the park, including the largest gey sers in the world.1 Sec (iEYSER.) These are grouped in six basins, the Norris Basin in the north cen tral part of the park on the Madison River. the Lower, Middle, and Upper Basins on the Firehole River between the Central and Madison Plateaus, and minor basins near Shoshone and Heart Lakes. Among the most celebrated individual geysers is the Giant. which at somewhat uncer tain intervals throws up a column of hot water five feet in diameter and over 200 feet high, and maintains it for over an hour, Old Faithful is the most regular in its intervals, spouting every sixty-five minutes a eohloin 12.5 feet bigli. Ex (4.141or Geyser has very long periods of (mkt, but its eruptions are extremely violent, the bed rock being sometimes torn up for many feet around it, while the volume of water ejected is enormous. Castle (leystr is one of the most beautiful, having a regular white cone situated in a glade sur rounded by dark green pine trees. Most of the geysers are irregular in their periods, Old Faith ful being nearly the only one whose eruptions can be safely predicted. Some are doubly pe riodic, having a smaller and a larger eruption at more or less regular intervals. New geysers occasionally burst forth, while others become extinct; thus one of the large geysers in the Norris Basin was formed suddenly in 1S78. See Plate with article GEYSER.