A little observation will show the student that this very muddy character of waters emerging from beneath the glacier is essentially peculiar to such streams as we have described. Ascending any of the principal valleys of Switzerland, he may note that some of the streams flow waters which carry little sediment even in times when they are much swollen, while others at all seasons have the whitish colour. A little further exploration, or the use of a good map, will show him that the pellucid streams receive no contributions of glacial water, while those which look as if they were charged with milk come, in part at least, from the ice arches. From some studies which the writer has made in Swiss valleys, it appears that the amount of erosion accomplished on equal areas of similar rock by the descent of the waters in the form of a glacier or in that of ordinary torrents differs greatly. Moving in the form of ice, or in the state of ice-confined streams, the mass of water applies very many times as much of its energy of position to grinding and bearing away the rocks as is accomplished where the water descends in its fluid state. The effect of the intense ice action above noted is rapidly to wear away the rocks of the valley in which the glacier is situated. This work is done not only in a larger measure but in a different way from that accomplished by torrents. In the case of the latter, the stream bed is embarrassed by the rubbish which comes into it; only here and there can it attack the bed rock by forcing the stones over its surface. Only in a few days of heavy rain each year is its work at all effective; the greater part of the energy of position of its waters is expended in the endless twistings and turnings of its stream, which result only in the development of heat which flies away into the atmosphere. In the ice stream, owing to its slow movement and to the detritus which it forces along the bottom, a vastly greater part of the energy which impels it down the slope is applied to rock cutting. None of the boulders, even if they are yards in diameter, obstruct its motion; small and great alike are to it good instruments wherewith to attack the bed rocks. The fragments are never left to waste by atmospheric decay, but are to a very great extent used up in mechanical work, while the most of the detritus which comes to a torrent is left in a coarse state when it is delivered to the stream; the larger part of that which the glacier transports is worn out in its journey. To a great extent it is used up in attacking the bed rock. In most cases the _debris_ in the terminal moraine is evidently but a small part of what entered the ice during its journey from the uplands; the greater part has been worn out in the rude experiences to which it has been subjected.