At its end there is a cliff of black, dirty ice, scarcely to be distinguished from rock at a little distance, from the base of which flows a turbid stream. This glacier is covered so completely with earth and stones that not a vestige of the ice can be seen unless we actually traverse its surface. Its appearance suggests the name of Black glacier, by which it is designated on the accompanying map.

The visitor to Haenke island has examples of at least two wellmarked types of glaciers in view: The small débris-covered icestreams, too small to reach the water, are typical of a large class of glaciers in southern Alaska, which are slowly wasting away and have become buried beneath débris concentrated at the surface by reason of their own melting. The Galiano glacier is a good example of this class. The Hubbard and Dalton glaciers are fine examples of another class of ice-streams which flow into the sea and end in ice-cliffs, and which for convenience we call tide-water glaciers. Nowhere can finer or more beautiful examples of this type be found than those in view from Haenke island.

FIGURE 1-Diagram illustrating the Formation of Icebergs.

The formation of icebergs from the undermining and breaking down of the ice-cliffs of the tide-water glaciers has already been mentioned. But there is another method by which bergs are formed a process even more remarkable than the avalanches that occur when portions of the ice-cliffs topple over into the sea. The ice-cliffs at the foot of the tide-water glaciers are really sea-cliffs formed by the waves cutting back a terrace in the ice. The submerged terrace is composed of ice, and may extend out a thousand feet or more in front of the visible part of the ice-cliffs. These conditions are represented in the accompanying diagram (figure 1), which exhibits a longitudinal section of the lower end of a tide-water glacier where it pushes out into the sea.

As the sea-cliff of ice recedes and the submerged terrace increases in breadth there comes a time when the buoyancy of the

15-NAT. GEOG. MAG., VOL. III, 1891.

ice at the bottom exceeds its strength, and pieces break off and rise to the surface. The water about the ends of the glaciers is so intensely muddy that the submerged ice-foot is hidden from view, and its presence would not be suspected were it not for the fragments occasionally rising from it. The sudden appearance of these masses of bottom ice at the surface is always startling. While watching the ice-cliffs and admiring the play of colors in the deep crevasses which penetrate them in every direction, or tracing in fancy the strange history of the silent river and wondering in what age the snows fell on the mountains, which are now returning to their parent, the sea, one is frequently awakened by a commotion in the waters below, perhaps several hundred feet in front of the ice-cliffs. At first it seems as if some huge sea-monster had risen from the deep and was lashing the waters into foam; but soon the waters part, and a blue island rises to the surface, carrying hundreds of tons of water, which flows down its sides in cataracts of foam. Some of the bergs turn completely over on emerging, and thus add to the tumult and confusion that attends their birth. The waves roll away in widening circles, to break in surf on the adjacent shores, and an island of ice of the most lovely blue floats serenely away to join the thousands of similar islands that have preceded it. The fragments of the glacier rising from the bottom in this manner are usually larger than those broken from the faces of the ice-cliffs, sometimes measuring 200 or 300 feet in diameter. Their size and the suddenness with which they rise would insure certain destruction of a vessel venturing too near the treacherous ice-walls.

At the time of our visit to Haenke island, the entire surface of Disenchantment bay and all of Yakutat bay as far southward as we could see formed one vast field of floating ice. Most of the bergs were small, but here and there rose masses which measured 150 by 200 feet on their sides and stood 40 or 50 feet out of the water. The bergs are divided, in reference to color, into three classes the white, the blue, and the black. The white ones are those that have fallen from the face of the ice-walls or those that have been sufficiently exposed to the atmosphere to become melted at the surface and filled with air cavities. The blue bergs are of many shades and tints, finding their nearest match in color in Antwerp blue. These are the ones that have recently risen from the submerged ice-foot, or have turned over owing to a change of position in the center of gravity. Rapid as is the