The Davidson Glacier, near the head of the canal, is one of the most interesting for purposes of study. It comes down from an unknown distance in the western interior, bearing two marked medial moraines upon its surface. On nearing tide-level, the valley through which it flows is about three-quarters of a mile in width; but, after emerging from the confinement of the valley, the ice spreads out over a fan-shaped area until the width of its front is nearly three miles. The supply of ice not being sufficient to push the front of the glacier into deep water, equilibrium between the forces of heat and cold is established near the water's edge. Here, as from year to year the ice melts and deposits its burdens of earthy _débris_, it has piled up a terminal moraine which rises from two hundred to three hundred feet in height, and is now covered with evergreen trees of considerable size. From Chilkat, at the head of Lynn Canal, to the sources of the Yukon River, the distance is only thirty-five miles, but the intervening mountain-chain is several thousand feet in height and bears numerous glaciers upon its seaward side. About forty miles west of Lynn Canal, and separated from it by a range of mountains of moderate height, is Glacier Bay, at the head of one of whose inlets is the Muir Glacier, which forms the chief attraction for the great number of tourists that now visit the coast of southeastern Alaska during the summer season. This glacier meets tide-water in latitude 58° 50', and longitude 136° 40' west of Greenwich. It received its name from Mr. John Muir, who, in company with Rev. Mr. Young, made a tour of the bay and discovered the glacier in 1879. It was soon found that the bay could be safely navigated by vessels of large size, and from that time on tourists in increasing number have been attracted to the region. Commodious steamers now regularly run close up to the ice-front, and lie-to for several hours, so that the passengers may witness the "calving" of icebergs, and may climb upon the sides of the icy stream and look into its deep crevasses and out upon its corrugated and broken surface. [Illustration: Fig. 12.--Map of Glacier Bay. Alaska, and its surroundings. Arrow-points indicate glaciated area.]