6G0 GLACIER-EROSION THEORY OF LAKE-BASINS. 



diately behind the enormous moraine of Ivrea and behind that of 

 Kivoli. If the cause •was equal to produce the effect in the other 

 instances, why did it wholly fail in these ? The onus probandi rests 

 with the advocates of erosion. The objections of the next class are 

 still more formidable. Glaciers move and erode under the law of 

 gravitation. Take the enormous Humboldt glacier of ' Peabody Bay ' 

 described by Dr. Kane. Between Capes Forbes and Agassiz it presents 

 a front of cliff 300 feet high along a stretch of sixty miles, forming a 

 stream of ice which is propelled uninterruptedly from the interior into 

 the sea. ' The general configuration of its surface showed how it 

 adapted itself to the inequalities of the basin-country beneath. There 

 was every modification of hill and valley, just as upon land ' (Kane, 

 p. 358). The stream of ice in motion in this case exerts a planing action 

 upon the rocks below by grinding, smoothing, and polishing. But 

 there is no penetrating effect along contracted lines of excavation. The 

 actual results of past conditions of the same nature are disclosed to us 

 in Norway at the present day on surfaces which were in the track of 

 ancient glaciers moving seawards. The area is ground, scooped, and 

 polished, but the major inequalities remain. 



The same conditions, under certain modifications, apply to glaciers 

 descending from mountain-chains. Instead of spreading out horizontally, 

 there they are pent up along contracted lines in Alpine valleys, accu- 

 mulated in masses several thousand feet in thickness, and therefore 

 exerting an enormous vertical pressure. The scouring, polishing, and 

 eroding effect is thus proportionately augmented, but the nature of the 

 action is not changed — it is still planing, not penetrating. Take the 

 chasm at the bottom of the incline, as in the case of the Lago Maggiore, 

 within a few feet of half a mile in depth. What new mechanical power 

 did the ice acquire there at the end of its journey of excavating so pro- 

 found an abyss? And, to repeat what I have already asked, could the 

 bottom stratum of ice, under the enormous vertical pressure to which 

 it was subjected, have moved up the incline in the given case ? Ob- 

 servation on modern glaciers by the most experienced of all glacialists, 

 the Swiss philosopher, has shown that a glacier at its terminus pushes 

 the frontal moraine ahead of it, but that it exerts no peculiar excavating 

 power at that point. So far as I am aware, not one of the Swiss geo- 

 logists has come forward as a convert to the erosion-hypothesis. To a 

 man, when they have spoken, they have pronounced against it. 



The view which I advocated was, that, both in the Alps and in the 

 Himalayahs, the lake-basins existed in the toansverse valleys before the 

 descent of the glaciers ; that, in the former case, they filled the lake- 

 basins, thus preventing them from being silted up, while in the latter, 

 glaciers not having descended, the basins remained open, and thus were 

 levelled by accumulated debris. Assuming that the basin-fissures 

 existed before the glaciers, the explanation would account for the con- 

 trary phenomena in the two mountain-chains. — The Reader, March 

 5, 1864. 



