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land in broad and shallow valleys their relatively gentle course is suddenly interrupted, and they at once cascade down the precipitous rock-walls to the sea. The side valleys that open upon a fiord are thus truncated by the steep mountain-wall as abruptly, Dr. Richter remarks, as if they had been cut across -with a knife.
Mountain-valleys of the V-shaped Alpine type are not wanting in the fjeld, but as they are followed inland towards the low water-partings of the plateau they soon lose their character and acquire softer features. The valleys of the fjeld-lands are for the most part broad and open, many lakes being scattered along the courses of the streams. We are here dealing, in fact, with a plateau lake-land, a region in which glacial erosion has been in excess of accumulation. It is through this gently undulating, highly iceworn plateau-land, with its shallow valleys, that the profound, chasm-like fiord-valleys have been cut to depths of 3000 to 6500 feet. That these enormous gorges are the work of erosion is not doubted by geologists, but the problem of their origin is nevertheless complex. Much has been written upon the subject, but no one has given a more lucid description of the actual facts, or a more intelligible explanation of their meaning, than Professor Richter, and him, therefore, we shall follow.
If we admit that a fiord is simply a partially drowned land-valley, and that the profound hollow in which it lies has been eroded by river action, how is it that the side streams have succeeded in doing so little work? Why should the erosion of the main or fiord-valleys be so immeasurably in advance of that of the lateral valleys? Obviously there must have been a time when the process of valley formation proceeded more rapidly along the lines of the present fiords and their head-valleys than in the side valleys which open upon these from the fjelds. At that time the work of rain and running water could not have been carried on equally over the whole land, otherwise we should find now a completely developed hydrographic system— not a plateau intersected by profound chasms, but an undulating mountain-land with its regular valleys. Nor can we believe that the present distinctive features of fjeld and fiord originated contemporaneously under a general ice-sheet. The wild rock-walls of the fiords, mostly ice-worn though they be, are not glacial features. Ice does not carve out cafions. According^ to Dr. Richter, the remarkable contrast between the deep valleys of the fiords and the shallow side valleys that open upon them from the fjelds—the profound erosion in the former, and the arrest of erosion on the plateau—admits of only one explanation. While rivers and rapid ice-streams, flowing in previously excavated valleys, were actively engaged in deepening these, the adjacent fjelds were buried under sheets of ndve'. At the time the fiords assumed their present characteristic features, the snow-line must have been depressed below its existing level, and large glaciers, preceded by torrential rivers, must eventually have ived down the fiords to the submarine bars that w appear at or near their entrances. Such condins obtained during certain stages of the Glacial :riod, both before and after the epoch of maximum aciation. While the fiords were being deepened, ■st by rivers and thereafter by large glaciers, the elds were undergoing effective glacial denudation, D that in time their configuration became greatly nodified. The mountain-ridges with their regular lydrographic system, as developed in preglacial :imes, were by and by broken up and replaced by the undulating rocky and lake-dappled plateaux which we now see. In short, while rivers and glaciers were deepening the great valleys and making their walls steeper, the intervening mountain-heights were gradually being reduced and levelled by denudation. Underneath the firn and ice of the plateau the erosion of deep gullies was at a standstill. It was somewhat otherwise in the Alps, where the hydrographic system, perfectly regular in preglacial times, was only slightly modified by subsequent glacial action. Yet even there erosion proceeded most rapidly along the chief lines of ice-flow. Were the great rock-basins of the principal Alpine valleys pumped dry we should find the mouths or openings of the side valleys abruptly truncated, and their waters cascading suddenly into the ice-deepened main valleys. For, as Dr. Wallace has shown, it is the present lake-surface, not the lakeboltom, that represents approximately the level of the preglacial valley. In a word, erosion proceeded most
r actively in the main valleys, the bottoms of which have been lowered for several hundred feet below the bottoms of the side valleys. Precisely the same phenomena are repeated in Scotland. Were all the water to disappear from the Highland lakes and sealochs, we should find waterfalls and cascades at the mouth of every lateral stream and torrent.
But another marked character of the fiords has yet to be mentioned. They are always deeper than the sea immediately outside, usually very much deeper. Some fiords show only one basin-shaped depression, while others may contain a succession of troughs. Frequently these basins are confined to the fiord, but in many cases they extend for less or greater distances beyond the entrance. In their form and disposition they are comparable to the great valleybasins of the Alps and similarly glaciated mountain tracts, and there can be little doubt that they have had a like origin. Were Scotland to be elevated so far as to run the sea out of her fiords, the latter would appear as mountain-valleys, each with one or more considerable lakes, in this and other respects exactly resembling the Highland glens that drain eastward into Loch Ness and the Moray Firth. The rock-basins in those glens, like the corresponding basins of the Alpine valleys, have often been modified by the accumulation of morainic ddbris and riverdetritus at their lower ends. Many Highland lakes, in short, are deeper than they would be were all the superficial deposits in the glens to be removed. We may well believe that the same is most likely to be true of the fiord-basins—the lips of the basins may in many cases be buried to some depth under morainic ddbris and more recent marine deposits. But that they are true rock-basins is shown by the fact that in not a few cases the sea-floor at the entrance is awash, ice-worn rocks every here and there rising to the surface and forming low islets and skerries. The fiord-basins in the depressed mountain-valleys of Scotland and Norway have obviously been ground out by large glaciers in the same way as the valleybasins of the Alpine lands. There are many other regions which show highly indented coasts, with long inlets stretching far inland, but these do not always contain basins. The latter only appear in places where large glaciers have formerly existed. Thus there are no fiord-basins in the Rias of Northern Spain, nor in the inlets of the Istrian and Dalmatian coasts, nor in the highly indented coast-lands of Australia and South-east China. But basins are always present in the ice-worn sounds of New Zealand, and in the true fiords of the higher latitudes of America. In a word, fiords are merely the drowned valleys of severely glaciated mountain tracts. A very slight depression of the land or rise of the sea-level would convert Loch Maree and Loch Lomond, and the great Alpine valleys that open upon the plains of the Po, into typical fiords.