When it

Such a line of débris is called a moraine. forms along the edge of the ice, it is called a lateral moraine. It is easy to see that, where glaciers come out from two valleys which are tributary to a larger valley, their inner sides must coalesce below the separating promontory, and the two lateral moraines will become united and will move onward in the middle of the surface of the glacier. Such lines of débris are called medial moraines. These are characteristic of all extensive glaciers formed by the union of tributaries. There is no limit to the number of medial moraines, except in the number of tributaries.

A medial moraine, when of sufficient thickness, protects the ice underneath it from melting; so that the moraine will often appear to be much larger than it really is what seems to be a ridge of earthy material being in reality a long ridge of ice, thinly covered with earthy débris, sliding down the slanting sides as the ice slowly wastes away Large blocks of stone in the same manner protect the ice from melting underneath, and are found standing on pedestals of ice, often several feet in height. An interesting feature of these blocks is that, when the pedestal fails, the block uniformly falls towards the sun, since that is the side on which the melting has proceeded most rapidly.

If the meteorological forces are so balanced that the foot of a glacier remains at the same place for any great length of time, there must be a great accumulation of earthy débris at the stationary point, since the motion of the ice is constantly bearing its lines of lateral and medial moraine downwards to be deposited, year by year, at the melting line along the front.

Such accumulations are called terminal moraines, and the process of their formation may be seen at the foot of almost any large glacier. The pile of material thus confusedly heaped up in front of some of the larger glaciers of the world is enormous.

The melting away of the lower part of a glacier gives rise also to several other characteristic phenomena. Where the foot of a glacier chances to be on comparatively level land, the terminal moraine often covers a great extent of ice, and protects it from melting for an indefinite period of time. When the ice finally melts away and removes the support from the overlying morainic débris, this settles down in a very irregular manner, leaving enclosed depressions to which there is no natural outlet. These depressions, from their resemblance to a familiar domestic utensil, are technically known as kettle-holes. The terminal moraines of ancient glaciers may often be traced by the relative abundance of these kettle-holes.

The streams of water arising both from the rainfall and from the melting of the ice also produce a peculiar effect about the foot of an extensive glacier. Sometimes these streams cut long, open channels near the end of the glacier, and sweep into it vast quantities of morainic material, which is pushed along by the torrential current, and, after being abraded, rolled, and sorted, is deposited in a delta about its mouth, or left stranded in long lines between the ice-walls which have determined its course. At other times the stream has disappeared far back in the glacier, and plunged into a crevasse (technically called a moulin), whence it flows onwards as a subglacial stream. But in this case the deposits might closely resemble those of the previous description. In both cases, when the ice has finally melted away, peculiar ridge-like deposits of sorted material remain, to mark the temporary line of drainage. These exist abundantly in most regions which have been covered with glacial ice, and are referred to in Scotland as kames, in Ireland as eskers, and in Sweden as osars. In this volume we shall call them kames, and the deltas spread out in front of them will be referred to as kame-plains.

With this preliminary description of glacial phenome

na, we will proceed to give, first, a brief enumeration and description of the ice-fields which are still existing in the world; second, the evidences of the former existence of far more extensive ice-fields; and, third, the relation of the Glacial period to some of the vicissitudes which have attended the life of man in the world.

The geological period of which we shall treat is variously designated by different writers. By some it is simply called the "post-Tertiary," or "Quaternary"; by others the term "post-Pliocene " is used, to indicate more sharply its distinction from the latter portion of the Tertiary period; by others this nicety of distinction is expressed by the term "Pleistocene." But, since the whole epoch was peculiarly characterised by the presence of glaciers, which have not even yet wholly disappeared, we may properly refer to it altogether under the descriptive name of "Glacial" period.

CHAPTER II.

EXISTING GLACIERS.

In Europe.-Our specific account of existing glaciers: naturally begins with those of the Alps, where Hugi, Charpentier, Agassiz, Forbes, and Guyot, before the middle of this century, first brought clearly to light the realityand nature of glacial motion.

According to Professor Heim, of Zürich, the total area. covered by the glaciers and ice-fields of the Alps is upwards of three thousand square kilometres (about eleven. hundred square miles). The Swiss Alps alone contain. nearly two-thirds of this area. Professor Heim enumerates 1,155 distinct glaciers in the region. Of these, 144 are in France, 78 in Italy, 471 in Switzerland, and 462 in. Austria.

Desor describes fourteen principal glacial districts in. the Alps, the westernmost of which is that of Mont Pelvoux, in Dauphiny, and the easternmost that in the vicin-ity of the Gross Glockner, in Carinthia. The most im-. portant of the Alpine systems are those which are grouped around Mont Blanc, Monte Rosa, and the Finsteraarhorn,. the two former peaks being upwards of fifteen thousand feet in height, and the latter upwards of fourteen thousand. The area covered by glaciers and snow-fields in the Bernese Oberland, of which Finsteraarhorn is the culminating point, is about three hundred and fifty square kilometres (a hundred square miles), and contains the Aletsch Glacier, which is the longest in Europe, extending twentyone kilometres (about fourteen miles) from the névé-field