"It seemed to begin at a distance, grow louder overhead where it filled the upper air, and suggested a medley of wind in the tops of pine trees, and in telegraph wires, the echo of bells after being repeated several times, the humming of a swarm of bees, and two or three other less definite sources of sound, making in all a composite which was not loud, but easily recognized, and not at all likely to be mistaken for any other sound in these mountain solitudes."[BK] [BK] "Overhead sounds in the vicinity of Yellowstone Lake." See Appendix E. No rational explanation has ever been advanced for this remarkable phenomenon. Its weird character is in keeping with its strange surroundings. In other lands and times it would have been an object of superstitious reverence or dread, and would have found a permanent place in the traditions of the people. CHAPTER XVIII. A TOUR OF THE PARK. _The Yellowstone Lake to Grand Cañon of the Yellowstone._ Distance seventeen miles. The road follows the Yellowstone River along the west bank all the way. Just after the tourist leaves the Lake Hotel, he will see on the right of the roadway a small monument. It was placed there, in 1893, by the United States Corps of Engineers to mark a position accurately determined from astronomical observations by the United States Coast and Geodetic Survey in 1892. It is of value as a point of reference in surveys and other similar work.[BL] [BL] Latitude, 44° 33' 16.1" north. Longitude, 110° 23' 43.1" west. Magnetic variation about 19° east. _Mud Volcano_ (7.5 miles) is a weird, uncanny object, but, nevertheless, a very fascinating feature and one which the tourist should stop and examine. It is an immense funnel-shaped crater in the side of a considerable hill on the west bank of the river. The mud rises some distance above a large steam vent in the side of the crater next the hill, and chokes the vent until the steam has accumulated in sufficient force to lift the superincumbent mass. As the imprisoned steam bursts forth, it hurls the mud with great violence against the opposite side of the crater, making a heavy thud which is audible for half a mile. These outbursts take place every few seconds. [Illustration: _Terry Engr. Co._ _Haynes, Photo., St. Paul._ Yellowstone River, between Lake and Falls.] A striking example of the strange commingling of dissimilar features in the hot springs districts is found in the _Grotto_, a spring of perfectly clear water, not far from the Mud Volcano. It is acted upon by the steam in a manner precisely similar to that of the Mud Volcano, but its waters issue directly from the rock, and are entirely clear. _Mud Geyser_, now rarely seen in action, was an important geyser twenty years ago. As it became infrequent in its eruptions, and tourists rarely saw them, the name was unconsciously, but mistakenly, transferred to the Mud Volcano, which has none of the characteristics of a geyser.