it in safety, and it will bear very heavy weights upon its surface, still moves slowly, and indeed almost imperceptibly, onward. The motion of the ice in glaciers is exceedingly slow-so slow that, notwithstanding the creaking and grinding sounds which are continually heard upon it, and the constant protrusion of its lower end through the soil, and even into the forests of the lower valleys, it was a long time before mankind could be convinced of the reality of it. It is now, however, not only positively known that it moves, but the rate of its progress has been exactly measured. In Switzerland, the average flow is about an inch an hour in the summer season. As, however, the motion varies very much according to the temperature of the air, in Greenland it must be much slower. It is well for voyagers passing to and fro across the Atlantic Ocean that it is so. FORMATION OF ICEBERGS. Whenever a glacier like those above described abuts upon the sea, the slow motion of the mass above and behind crowds the termination of it out over the water, until undermined by the waves, and borne down by the superincumbent weight, immense masses break off and fall over and are borne away by the currents and tides. The fall of one of these mountains produces, in the stillness of the Arctic night, a sound like that of thunder, and the vast undulation of the sea occasioned by the fall rocks the ships of whalemen or of explorers at a distance of many miles in the offing. It is thus that the icebergs are formed, which add so much to the danger of crossing the Atlantic, and which probably explain the mystery in which is involved the fate of the large number of vessels that, after leaving the land in safety, are never heard of again. These icebergs, however, so dangerous to navigators on the open sea, are the friends and protectors of ships exploring the Arctic shores, affording them, as they so often do, a sure and efficient shelter from fields and packs of ice which come sweeping over the sea with a slow but inconceivably destructive force, that nothing but a rock or an iceberg can withstand. ICE FORMED UPON THE SEA. The ice that is formed upon the sea is flat and level and comparatively thin. It is seldom more than from ten to fifteen feet in thickness. It drifts to and fro through the Arctic seas wherever the winds and the currents bear it, moving always with immense force, sometimes in vast and contin uous fields, sometimes in broken packs wedged together and piled up in lofty heaps, and sometimes in detached and scattered floes. It carries with it stones, drift wood, and animals of various kinds. The drift wood it collects for itself from the supplies brought by the currents of the ocean from more southern climates. The stones fall upon it from the icebergs. Animals travel over it when it is fast to the shore, and then, when the tide or the wind or the set of the current breaks it up, they are taken with it and borne away. CURRENTS IN THE NORTHERN SEAS. In other parts of the world the movements of the ocean in the flow of tides and currents are silent and unseen, but in the Arctic seas the presence of the ice makes them all manifest to the senses of the observer in the most imposing manner. The majestic march of the immense floes, as they are seen sometimes, grinding their resistless way along a rocky shore, sometimes struggling against each other in a conflict continued for many hours, and piling up immense heaps of broken ice along the line of collision for many miles; sometimes crowding through narrow passages, and then again sweeping down in an immense stream, hundreds of leagues in length, toward the open sea, pre |