A glacier is a river of ice,--really and truly a river of ice,--sometimes two or three miles wide, and fifteen or twenty miles long, with many branches coming into it. Its bed is a steep valley, commencing far up among the mountains in a region of everlasting ice and snow, and ending in some warm and pleasant valley far below, where the warm sun beats upon the terminus of it and melts the ice away as fast as it comes down. It flows very slowly, not usually more than an inch in an hour. The warm summer sun beams upon the upper surface of it, melting it slowly away, and forming vast fissures and clefts in it, down which you can look to the bottom, if you only have courage to go near enough to the slippery edge. If you do not dare to do this, you can get a large stone and throw it in; and then, if you stand still and listen, you hear it thumping and thundering against the sides of the crevasse until it gets too deep to be any longer heard. You cannot hear it strike the bottom; for it is sometimes seven or eight hundred feet through the thickness of the glacier to the ground below. The surface of the glacier above is not smooth and glassy like the ice of a freshly-frozen river or pond; but is white, like a field of snow. This appearance is produced in part by the snow which falls upon the glacier, and in part by the melting of the surface of the ice by the sun. From this latter cause, too, the surface of the glacier is covered, in a summer's day, with streams of water, which flow, like little brooks, in long and winding channels which they themselves have worn, until at length they reach some fissure, or crevasse, into which they fall and disappear. The waters of these brooks--many thousands in all--form a large stream, which flows along on the surface of the ground under the glacier, and comes out at last, in a wild, and roaring, and turbid torrent, from an immense archway in the ice at the lower end, where the glacier terminates among the green fields and blooming flowers of the lower valley.