Abstract
PROF. T. G. BONNEY, F.R.S., read a paper to the last meeting of the Royal Geographical Society on the question, Do glaciers excavate? In view of the correspondence recently published in our columns the arguments adduced in support of the negative conclusions may be cited in some detail. The question of the glacial origin of lakes involves many separate considerations. While lakes undoubtedly abound in regions now or formerly subjected to glaciation, many of these are formed by the damming of valleys by moraine heaps, or by extensive landslips. The school of Sir A. Ramsay affirm that glaciers are powerful excavating agents, and that there is no other agent but ice competent to form a rock-basin. The last argument breaks down when one considers the number of depressions of all sizes gradually increasing from mere volcanic craters to those of the Jordan Valley and the Caspian Sea, in the formation of which ice could have had no part. The argument that Greenland alone holds the key to the phenomena of glaciation breaks down, for the Alps were once the seat of a vast icesheet, which over-rode all the minor inequalities of the surrounding country, and of which the existing glaciers are the shrunken remnant. Thus the Alpine valleys should serve to show the typical results of ice-action on the land. This is the sum of their evidence: toothed prominences have been broken or rubbed away, the rough places have been made smooth, the rugged hill has been reduced to rounded slopes of rock (like the backs of plunging dolphins). But the crag remains a crag, the buttress a buttress, and the hill a hill; the valley also does not alter its leading outlines, the V like section so characteristic of ordinary fluviatile erosion still remains; all that the ice has done has been to act like a gigantic rasp; it has modified, not revolutionised, it has moulded, not regenerated. No sooner do we come to study in detail the effects of the ancient glaciers in the upper valleys of the Alps than we are struck by their apparent as erosive agents. Here, where the ice has lingered longest, just beneath the actual glacier we see that a cliff continues to exist. Again and again in a valley we may find that on the lee side of prominences crags still remain, sometimes in sufficient frequency to be marked features in the scenery. The Haslithal is an excellent and representative example.
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The Action of Glaciers on the Land. Nature 47, 521–522 (1893). https://doi.org/10.1038/047521a0
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DOI: https://doi.org/10.1038/047521a0