The piling up of these mountain-snows is like the processes of a geological epoch in the steady growth by deposit. There is this difference, however, that ice formed in this manner is not, like rock, hard and unyielding, but, like putty, is, in a measure, ductile. In fact, it _flows_ downward, and the superabundant accumulations find their way thus to the ocean. It is estimated that the snows of the Alps would increase the altitude of those mountains four thousand feet in a thousand years but for this strange ductile property of ice. As we have before seen, an ice-stream is, in effect, a frozen river, flowing at a very slow, but still at a very perceptible rate. The rate of flow in the Alps, variously estimated by different explorers and at different places, where there were different degrees of descent, is from six to fourteen inches daily. In Greenland the rate, as determined by me, is about from five to eight inches daily. The Greenland glaciers possess another marked difference from those of the Alps. The ends of the latter, descending into a lower and warmer level, are melted off, and disappear as the end of a tallow candle would disappear if held near a hot stove. Before this takes place, the ice, descending through the valley, conforms to all its inequalities, and the actual river which ultimately takes its rise from the glacier front does not more readily mould itself to the rocky bed over which it flows—widening and contracting, deepening or shoaling as the river-bed expands and narrows, or increases and diminishes its declination. An ice-stream, or glacier, like the river, has therefore its cascades, its rapids, its broad lagoons (so to speak), and its smooth, steady, even flow. It carries rocks along with it upon its surface (rocks which have fallen upon it from the cliffs along its sides), as the river carries sticks of wood and, when the ice melts, these rocks fall in front, and, rolling down the valley, form _moraines_. But with the Greenland glaciers the result is different. The end of the glacier never descends into a level that is warm enough to melt away the end of it, as in the Alps, but it reaches the sea in all the glory of its cold and crystal hardness. When this happens, its end penetrates the water, and makes a coast-line of ice. The temperature of Greenland, down even to the water-level, is too low to allow of any considerable melting, but the result is the same. A fragment breaks off from the glacier and floats away upon the ocean, and is drifted to and fro with the ocean currents. Rocks which may have fallen upon the glacier from the cliffs are inclosed within it, or are carried upon the top of it.