For all these reasons, he adds, the medial and lateral moraines are scarcely conspicuous on the glaciers of Spitzbergen; a number of stones and boulders may be seen along their sides, and sometimes in their centre, but the ice is never hidden, as in the Alps, under the mass of débris accumulated upon it. As for the terminal moraines, they must be sought at the bottom of the sea, since the terminal escarpment nearly always overhangs it. Hence, the blocks of stone fall simultaneously with the blocks of ice, and form a submarine frontal moraine, of which the two extremities are occasionally visible upon the shore. In a previous chapter we have alluded to the manner in which icebergs are formed by the detachment from the seaward extremity of the glacier of huge masses of ice, which the current carries out into the open sea. To the description already given, we may here add that which Charles Martins furnishes in his valuable and interesting record of persevering scientific enterprise, “Du Spitzberg au Sahara”:--In Spitzbergen, he says, the glacier, after a traject of more or less considerable duration, reaches the sea. If the shore be rectilineal, it advances no further; but, in the recess of a bay, where the shore is curved, it continues its progression, supporting its bulk on the sides of the bay, and advancing above the water, which it overhangs. This is easily understood. In summer the sea-water at the bottom of the bays is always at a temperature a little above 32°; on coming in contact with this comparatively warm water the glacier melts, and, at low tide, an interval is perceptible between the ice and the surface of the water. The glacier being no longer supported, partially crumbles and gives way; immense blocks detach themselves, fall into the sea, disappear beneath the water, reappear revolving on their own axes, and oscillate for a few moments until they have taken up their position of equilibrium. The blocks thus detached from the floating masses, of all sizes and shapes, are called icebergs. [Illustration: STEAMER “CHARGING” AN ICEBERG, UPERNAVIK, GREENLAND.]