Here we have a witness's description of the process which clouds the career of the Excelsior Geyser. The enlargement of the vent eventually gave unrestrained passage to the imprisoned steam. The geyser ceased to play. To-day the Excelsior Spring is one of the largest hot springs in the Yellowstone and the world; its output of steaming water is constant and voluminous. Thus again we find relationship between the hot spring and the geyser; it is apparent that the same vent, except perhaps for differences of internal shaping, might serve for both. It was the removal of restraining walls which changed the Excelsior Geyser to the Excelsior Spring. For many years geyser action remained a mystery balanced among conflicting theories, of which at last Bunsen's won general acceptance. Spring waters, or surface waters seeping through porous lavas, gather thousands of feet below the surface in some pocket located in strata which internal pressures still keep hot. Boiling as they gather, the waters rise till they fill the long vent-hole to the surface. Still the steam keeps making in the deep pocket, where it is held down by the weight of the water in the vent above. As it accumulates this steam compresses more and more. The result is inevitable. There comes a moment when the expansive power of the compressed steam overcomes the weight above. Explosion follows. The steam, expanding now with violence, drives the water up the vent and out; nor is it satisfied until the vent is emptied. Upon the surface, as the geyser lapses and dies, the people turn away to the Inn and luncheon. Under the surface, again the waters gather and boil in preparation for the next eruption. The interval till then will depend upon the amount of water which reaches the deep pocket, the size of the pocket, and the length and shape of the vent-hole. If conditions permit the upward escape of steam as fast as it makes in the pocket, we have a hot spring. If the steam makes faster than it can escape, we have a geyser. [Illustration: _From a photograph by Haynes_ THE EXCELSIOR GEYSER WHICH BLEW OUT IN 1888; YELLOWSTONE] [Illustration: _From a photograph by Haynes_ ONE OF THE TERRACES AT MAMMOTH HOT SPRINGS; YELLOWSTONE] III So interesting are the geysers and their kin that, with their splendid wilderness setting, other glories seem superfluous. I have had my moments of impatience with the Grand Canyon of the Yellowstone for being in the Yellowstone. Together, the canyon and the geysers are almost too much for one place, even perhaps for one visit. One can only hold so much, even of beauty, at once. Spectacles of this quality and quantity need assimilation, and assimilation requires time. Nevertheless, once enter into sympathetic relations with the canyon, once find its heart and penetrate its secret, and the tables are quickly turned. Strangely, it now becomes quite easy to view with comparative coolness the claims of mere hot-water wonders.