It is in this way that the consolidation of the snows takes place in the Arctic as in the higher Alpine regions. The deeper layers of the _névé_ are converted into more or less perfect ice by the pressure of the superjacent layers; and further, they are made to assume the shape of the valley which they fill, by the slow and continuous pressure of its sides. In glaciers, as Professor Tyndall points out, we have ample illustrations of rude fracture and regelation; as, for example, in the opening and closing of crevasses. The glacier is broken on the cascades, and mended at their bases. When two branch glaciers lay their sides together, the regelation is so firm that they begin immediately to flow in the trunk glacier as in a single stream. The medial moraine gives no indication by its slowness of motion that it is derived from the sluggish ice of the sides of the branch glaciers. We may sum up the regelation theory in few words. The ice of glaciers changes its form and retains its continuity under _pressure_ which keeps its particles together. But when subjected to _tension_, sooner than stretch, it _breaks_, and behaves no longer as a viscous body. These are Professor Tyndall’s words, and the fact which they embody it would be difficult to set forth more clearly or more concisely. [Illustration: A POLAR GLACIER.] Having said thus much of the structure, causes, characteristics, and movement of glaciers, we proceed to consider some of the more remarkable of those which are situated in the Arctic World. The glaciers of the Polar Regions do not differ in structure or mode of formation from those of other countries. Yet they possess some peculiar features, and to a superficial observer might seem independent of the physical laws we have attempted to explain. That this is not the case has been shown by Charles Martins, who carefully studied the glaciers of Spitzbergen on the occasion of the exploring voyage of the _Recherche_ to that island, and has demonstrated that their differences are but a particular case of the general phenomenon. As special characters he points out, first, the rarity of needles and prisms of ice, which he attributes to the slight inclination and the uniformity of the slopes, as well as to the diminution of the solar heat, which, even in the long summer days, does not melt the surface. There are no rills or streams capable of hollowing out crevasses and moulding protuberances or projections. But transversal crevasses produced by the movement of the glaciers are numerous, and these are often very wide and very deep. [Illustration: GLACIER, ENGLISH BAY, SPITZBERGEN.]