CHAPTER IX. ON MORAINES.
Now, in order clearly to understand the formation of moraines, I must first say a little more about the movement of glaciers and the débris which they bring down.
I have sometimes heard unthinking persons remark that the snowfall of each winter must tend to increase the height of snow-peaks. This observation shows that such people entirely overlook the four great factors in the maintenance of a uniform height on mountain summits, namely, melting, evaporation (which, in the dry air of the heights, is a very powerful factor in causing the disappearance of snow), glaciers, and avalanches. It is to the two latter of these that we must look for the construction of moraines, in which work they are very largely aided by two other factors, frost and rain. The glacier, starting in its infant purity from some white, unsullied peak, loses, before many years have past, its spotless character. The wintry frosts, gathering into iron bonds the streams which trickle down the mountain-sides, expand the water in freezing, and shatter the rocks with a force that the most solid cliffs cannot resist. Broken and weathered fragments are washed down from the slopes on every fall of rain, and dropping on to the once unspotted bosom of the glacier, swell the burden which is gradually laid upon it with advancing years. Spring after spring, furious avalanches rush down, laden with earth and stones, which they fling recklessly upon the now begrimed edges of the icy stream. The winds and storms, too, contribute their share of dust and sand, and as the glacier still flows on, shrunken in size and laden with heaps of earth and rocks, at length it lays itself to rest, a mass of dirty ice and stones, in the valley towards which it has been ceaselessly progressing.
The glacier of the Alps which comes farthest down into the lower regions is the Grindelwald glacier, which descended to 1080 metres above sea-level in 1870, while that which presents the largest surface is the Aar glacier, and the longest is the Aletsch. Heim gives an estimate, in his valuable work on glaciers, of the number of glaciers existing in Europe, dividing them into those of the first and second order.
The list is as follows:—
| 1st Order. | 2nd Order. | Total. | |
| Switzerland | 138 | 333 | 471 |
| Austria | 71 | 391 | 462 |
| France | 25 | 119 | 144 |
| Italy | 15 | 63 | 78 |
| —— | —— | ——— | |
| 249 | 906 | 1,155 |
Glaciers have regular periods during which they advance or retreat. Many persons who visited the Mer de Glace some twenty or more years ago remember that it then came down nearly to the level of the valley of Chamonix, while the Rhone glacier reached almost to where the lower hotel now stands. In old days, too, the two arms of the Fee glacier united below the Gletscher alp, so that the cows had to pass across the ice in order to reach their summer pastures. A period of advance is always preceded for some years by a noticeable swelling of the upper portions of glaciers; this, of course, is quite what one would expect. A succession of cold, rainy summers and exceptionally snowy winters eventually causes an increase in the glaciers, and the reverse has naturally the contrary effect.
You have learnt that a moraine is a mixture of earth and stones which is borne down by a glacier, and you know how all this débris has accumulated on the ice, chiefly by means of the shattering power of frost on the rocks. Now let us notice the position which moraines assume on a glacier like, say, the Morteratsch. As I have said, persons unaccustomed to the mountain world, and thus unable to estimate the relative sizes of objects seen at a distance, have been known to inquire, when ascending Piz Languard, if the dark streak down the centre of the Morteratsch glacier is a path. They are astonished to learn that it is about fifty feet or more broad, and perhaps twenty feet high in the centre. It is, in fact, neither more nor less than a moraine, and belongs to that class known as medial moraines. Each glacier has a moraine on either side of it, and when two glaciers unite, their lateral moraines join and form a medial moraine. The moraine at the end of a glacier (terminal moraine) is almost entirely formed of the earth and stones which fall off the end of a glacier, and not, as used to be supposed, by any pushing or scooping of the base of the glacier.
In fact, the erosive power of a glacier is infinitesimal as compared with that of water. Dr. Heim cites various examples to show that a glacier leaves undisturbed much of what it finds in its way, and he says that the Forno glacier, which some years ago greatly retreated and left blocks of itself covered with débris behind, rapidly advanced once more in 1884 over the old accumulations at its base, but did not disturb them in any way. Many of our readers will have noticed the many glacier-worn rocks in the Engadine valley; they are especially abundant near Maloja.