Modern Geography

by Marion I. Newbigin

In the last chapter we have spoken of the moulding of the surface of the earth by means of running water and the agents summed up in the term “weathering.” The process is sometimes called “normal erosion,” to distinguish it from that other form of surface moulding in which ice and frost play a prominent part. At the present time ice, in the form of ice-sheets or glaciers, is confined to relatively small areas of the globe, so that we are justified in regarding its action as exceptional when compared with the work of running water. It is, however, well known that this limitation of the field of action of ice is very recent, and that during a period which geologically is only yesterday, a much greater part of the surface than at present was ice-clad.

In point of fact, much of Europe, especially the northern parts and those regions which lie close to the lofty mountain chains, much of North America, and, probably, considerable parts of the southern hemisphere, were subjected to the action of ice so recently that the processes of normal erosion have not had time to obliterate, hardly even to blur, the tracks which the ice left.

The results of the great extension of ice action in that period which geologists call Pleistocene were twofold. In the first place, as the result of the presence of the ice-sheet, we have vast accumulations of débris spread over the lower grounds. These accumulations sometimes form great sheets of boulder clay; sometimes they are collected into the curious sandy and gravelly mounds called kames which in parts of, e. g. Scotland, have a great extension; sometimes they have formed great heaps of material at the entrances of valleys. Again, these deposits have sometimes blocked valleys and so formed lakes, and they have supplied the post-glacial rivers with a vast amount of material which has been used to scour out the river-beds, and has been often re-sorted and re-arranged by running water.

Secondly, the fact that the northern region and the high grounds further south, in both Europe and North America, have been recently clad in ice is associated with many peculiarities of surface form, some of which have exercised a marked influence on human settlements and ways of communication.

These peculiarities of surface moulding have been the object of singularly detailed study in late years, and from this detailed study many interesting facts have emerged. It may be well to state at once that this study has been largely stimulated by the fact that there is at present a great want of unanimity of opinion as to the exact cause of these peculiarities of form. According to one school ice is a more powerful eroding agent than water; according to another its action is largely conservative, and its power of erosion is slight as compared with that of water.

The beginnings of a possible solution of the problem are perhaps to be seen in the suggestions of those who seek the causes of the peculiar features of glaciated regions in the way in which running water works when it is controlled and modified by the existence of ice; but we must admit that, on the whole, the conflict is still hot and many members of the opposing schools will have no compromise.

To the geographer, however, the very fierceness of the controversy has been useful. The question as to the exact part played respectively by water and by ice in surface moulding is really a question for the geologist. It is, however, of great importance to the geographer that recently glaciated surfaces should be studied from every point of view, for from this detailed study are emerging many important generalisations. We shall, therefore, in this chapter only touch very lightly upon the actual points in dispute, but shall lay stress upon the interesting facts admitted by both parties.

When the conception of a just-vanished period of great glaciation was being established by the labours of many geologists, stress was naturally laid upon the obvious resemblances between parts of, e. g. Scotland and Wales, and those parts of the Alps which have been exposed by the retreat of the existing glaciers. Thus we find that most of the text-books emphasise the occurrence of perched blocks, of erratics, i. e. of blocks of rock which must have been carried from a distance, of the phenomenon of crag and tail, of giants’ kettles, and so on. All these are of more geological than geographical importance; they do not in themselves greatly affect the distribution of other phenomena over the surface. We shall not, therefore, stop to consider them in detail. It is otherwise with those indications of recent glaciation which have been studied within the last few years, and they demand the geographer’s most careful consideration.