The glaciers are formed from the avalanches which fall into the upper valleys in cases where the valleys are so deep and narrow and so secluded from the sun that the snows which slide into them cannot melt. In such case, the immense accumulations which gather there harden and solidify, and become ice; and, what is very astonishing, the whole mass, solid as it is, moves slowly onward down the valley, following all the turns and indentations of its bed, until finally it comes down into the warm regions of the lower valleys, where the end of it is melted away by the sun as fast as the mass behind crowds it forward. It is certainly very astonishing that a substance so solid as ice can flow in this way, along a rocky and tortuous bed, as if it were semi-fluid; and it was a long time before men would believe that such a thing could be possible. It was, however, at length proved beyond all question that this motion exists; and the rate of it in different glaciers at different periods of the day or of the year has been accurately measured. If you go to the end of the glacier, where it comes out into the lower valley, and look up to the icy cliffs which form the termination of it, and watch there for a few minutes, you soon see masses of ice breaking off from the brink and falling down with a thundering sound to the rocks below. This is because the ice at the extremity is all the time pressed forward by the mass behind it; and, as it comes to the brink, it breaks over and falls down. This is one evidence that the glaciers move. But there is another proof that the ice of the glaciers is continually moving onward which is still more direct and decisive. Certain philosophers, who wished to ascertain positively what the truth was, went to a glacier, and, selecting a large rock which lay upon the surface of it near the middle of the ice, they made a red mark with paint upon the rock, and two other marks on the rocks which formed the shore of the glacier. They made these three marks exactly in a line with each other, expecting that, if the glacier moved, the rock in the centre of it would be carried forward, and the three marks would be no longer in a line. This proved to be the case. In a very short time the central rock was found to have moved forward very perceptibly. This was several years ago. This rock is still on the glacier; and the red mark on it, as well as those on the shores, still remains. All the travellers who visit the glacier look at these marks and observe how the great rock on the ice moves forward. It is now at a long distance below the place where it was when its position was first recorded.