So abundant are the evidences of grand volcanic action throughout the lake basin that it has been looked upon by scientists as the remains or centre of one enormous crater forty miles across! Dr. Hayden, the profound geologist, who was sent professionally by the government to report upon the Park, declares it to have been the former scene of volcanic activity as great as that of any part of this planet, a conclusion which the observer of to-day is quite ready to admit, inasmuch as the subsidence has yet left enough of the original forces to demonstrate the sleeping power which still lurks restlessly beneath the soil. We wonder, standing amid such remarkable surroundings, how many centuries have passed since the valley assumed its present shape. Everything is indicative of high antiquity, and it is probably rather thousands than hundreds of years since this volcanic centre was at its maximum power and activity. The valley has been partly excavated out of ancient crystalline rocks, partly out of later stratified formations, and partly from masses of lava that were poured forth during a succession of ages which make up the different epochs of the earth’s long history. The lowest level of the Park is about six thousand feet above the sea, and the average elevation, independent of mountains, is much over this estimate. It is very properly designated as the summit of the continent, and gives rise to three of the largest rivers in North America, namely: on the north side are the sources of the Yellowstone; on the west, three of the forks of the Missouri; and on the southwest are the sources of the Snake River, which flows into the Columbia, and thence to the distant Pacific Ocean. If possible, before leaving the neighborhood, the visitor should ascend Mount Washburn, the highest point of observation within the great reservation, a feat easily accomplished on horseback. Such an excursion is particularly desirable since all the scenery of the Park is circumscribed while we are at the level of its springs, geysers, and lakes. The grand view from this elevation will repay all the time and effort expended in its accomplishment. Its height above the base is five thousand feet, its height above the sea five thousand more. A clear day is absolutely necessary for the proper enjoyment of such an excursion, in order to bring out fairly the panorama of forests, lakes, prairies, and mountains, decked by the golden glory of the sunshine. In some directions the vision reaches a hundred and fifty miles through space. Here, on the summit of Mount Washburn, we virtually stand upon the apex of the North American continent, if we except one or two of the sky-reaching peaks of the Territory of Alaska.