Two hundred and thirty miles east of the Cavern, Clark inscribed his name and the date, July 25, 1806, upon the face of a prominent butte known as Pompey's Pillar. This would have been a far more appropriate monument to the most important of American explorations than the limestone cave. In fact, the Department of the Interior once attempted to have it proclaimed a national monument; the fact that it lay within an Indian allotment prevented. The entire course of this great expedition should be marked at significant points by appropriate national monuments. WIND CAVE NATIONAL PARK In the southwestern corner of South Dakota, on the outskirts of the Black Hills, is one of the most interesting limestone caverns of the country. It was named Wind Cave because, with the changes of temperature during the day, strong currents of wind blow alternately into and out of its mouth. It has many long passages and fine chambers gorgeously decorated. It is a popular resort. The United States Biological Survey maintains a game-preserve. JEWEL CAVE NATIONAL MONUMENT Northwest of Wind Cave, thirteen miles west and south of Custer, South Dakota boasts another limestone cavern of peculiar beauty, through whose entrance also the wind plays pranks. It is called Jewel Cave because many of its crystals are tinted in various colors, often very brilliantly. Under torchlight the effect is remarkable. Connecting chambers have been explored for more than three miles, and there is much of it yet unknown. OREGON CAVES NATIONAL MONUMENT In the far southwestern corner of Oregon, about thirty miles south of Grant's Pass, upon slopes of coast mountains and at an altitude of four thousand feet, is a group of large limestone caves which have been set apart by presidential proclamation under the title of the Oregon Caves National Monument. Locally they are better known as the Marble Halls of Oregon. There are two entrances at different levels, the passages and chambers following the dip of the strata. A considerable stream, the outlet of the waters which dissolved these caves in the solid limestone, passes through. The wall decorations, and, in some of the chambers, the stalagmites and stalactites, are exceedingly fine. The vaults and passages are unusually large. There is one chamber twenty-five feet across whose ceiling is believed to be two hundred feet high. MOUNT OLYMPUS NATIONAL MONUMENT For sixty miles or more east and west across the Olympian Peninsula, which is the forested northwestern corner of Washington and the United States between Puget Sound and the Pacific Ocean, stretch the Olympian Mountains. The country is a rugged wilderness of tumbled ranges, grown with magnificent forests above which rise snowy and glaciered summits. Its climax is Mount Olympus, eight thousand one hundred feet in altitude, rising about twenty-five miles equidistant from the Strait of Juan de Fuca upon the north and the Pacific Ocean upon the west.