Some twenty miles above the head of the lake is the celebrated _Two-Ocean Pass_, long known to the early trappers. It is probably the most remarkable example of such a phenomenon in the world. Although the fact of its existence was asserted and stoutly maintained by Bridger for many years prior to the discovery of the Park region, it was generally disbelieved until Captain Jones crossed the pass in 1873. It has since been visited and described by Hayden in 1878, by Hague in 1884, and by Prof. Evermann of the United States Fish Commission in 1891. The following facts and map are taken from Prof. Evermann's report: [Illustration: _Terry Engr. Co._ Sketch of Two-Ocean Pass.] The pass is in a nearly level grassy park hemmed in by the surrounding hills, and is 8,150 feet above the level of the sea. Its extreme length is about one mile and its extreme breadth about three-fourths of a mile. From the north a stream issues from a cañon, _a_, and divides at _b_, part flowing to Atlantic Creek and part to Pacific Creek. A similar stream, _c_, with a similar division, _d_, comes from the south. At extreme low water, these divisions may possibly disappear and all the water flow either one way or the other. But at ordinary and high stages the water flows both ways. These streams are by no means insignificant rivulets, but substantial water-courses capable of affording passage to fish of considerable size. Here, then, we have the very interesting phenomenon of a single stream upon the summit of the continent dividing and flowing part one way and part the other, and forming a continuous water connection between the Atlantic and Pacific Oceans over a distance of nearly 6,000 miles. A most singular and interesting acoustic phenomenon of this region, although rarely noticed by tourists, is the occurrence of strange and indefinable overhead sounds. They have long been noted by explorers, but only in the vicinity of Shoshone and Yellowstone Lakes. They seem to occur in the morning, and to last only for a moment. They have an apparent motion through the air, the general direction noted by writers being from north to south. The following descriptions are from the pens of those who have given some study to these strange sounds. Prof. S. A. Forbes says: "It put me in mind of the vibrating clang of a harp lightly and rapidly touched high up above the tree tops, or the sound of many telegraph wires swinging regularly and rapidly in the wind, or, more rarely, of faintly heard voices answering each other overhead. It begins softly in the remote distance, draws rapidly near with louder and louder throbs of sound, and dies away in the opposite direction; or it may seem to wander irregularly about, the whole passage lasting from a few seconds to half a minute or more."[BJ] [BJ] "Overhead sounds in the vicinity of Yellowstone Lake." See Appendix E. Mr. Edwin Linton thus describes it: