because it is notoriously, and before men's eyes now, carrying great stones hundreds of miles, and scratching and rounding them also; carrying vast deposits of mud, too, and mixing up mud and stones just as we see them in the brick-pits,--Would not our common sense have a right to try that explanation?--to suspect that this force, which we do not see at work in Britain now, may have been at work here ages since? That would at least be reasoning from the known to the unknown. What state of things, then, do we find among the highest mountains; and over whole countries which, though not lofty, lie far enough north or south to be permanently covered with ice? We find, first, an ice-cap or ice-sheet, fed by the winter's snows, stretching over the higher land, and crawling downward and outward by its own weight, along the valleys, as glaciers. We find underneath the glaciers, first a moraine profonde, consisting of the boulders and gravel, and earth, which the glacier has ground off the hillsides, and is carrying down with it. These stones, of course, grind, scratch, and polish each other; and in like wise grind, scratch, and polish the rock over which they pass, under the enormous weight of the superincumbent ice. We find also, issuing from under each glacier a stream, carrying the finest mud, the result of the grinding of the boulders against each other and the glacier. We find, moreover, on the surface of the glaciers, moraines superieures--long lines of stones and dirt which had fallen from neighbouring cliffs, and are now travelling downward with the glaciers. Their fate, if the glacier ends on land, is what was to be expected. The stones from above the glacier fall over the ice-cliff at its end, to mingle with those thrown out from underneath the glacier, and form huge banks of boulders, called terminal moraines, while the mud runs off, as all who have seen glaciers know, in a turbid torrent. Their fate, again, is what was to be expected if the glacier ends, as it commonly does in Arctic regions, in the sea. The ice grows out to sea-ward for more than a mile sometimes, about one-eighth of it being above water, and seven-eighths below, so that an ice-cliff one hundred feet high may project into water eight hundred feet deep. At last, when it gets out of its depth, the buoyancy of the water breaks it off in icebergs, which float away, at the mercy of tides and currents, often grounding again in shallower water, and ploughing the sea-bottom as they drag along it. These bergs carry stones and dirt, often in large quantities; so that, whenever a berg melts or capsizes, it strews its burden confusedly about the sea-floor.