September i, 1910] 



NATURE 



277 



Caucasus or of the Himalayas differs in scale ratlier than 

 In kind from that of the Alps. Thus the amount of 

 abrasion varies, other things being equal, with the lati- 

 tude. The grinding away ot ridges and spurs, the smooth- 

 ing of the walls of troughs,' is greater in .Norway than 

 in the .Alps ; it is still greater in Greenland than in Norway, 

 and it is greatest of all in the Antarctic, according to the 

 reports ol the expeditions led by Scott and Shackleton. 

 But even in Polar regions, under the most favourable con- 

 ditions, the dominant outlines of the mountains, as shown 

 in the numerous photographs taken by both parties, and 

 in Dr. Wilson's admirable drawings, differ in degree rathei 

 than in kind from those of mid-turopean ranges. It has 

 been asserted that the parallel sides of the larger Alpine 

 valleys — such as the Rhone above Martigny, the Liitschine 

 near Lauterbrunnen, and the \'al Bedretto below Airolo — 

 prove that they have been made by the ice-plough rather 

 than by running water ; but in the first I am unable to 

 discern more than the normal effects of a rather rapid 

 river which has followed a trough of comparatively soft 

 rocks; in the second, only the cliffs marking the channel 

 cut by a similar stream through massive limestones — cliffs 

 like those which elsewhere rise up the mountain flanks far 

 above the levels reached by glaciers ; while in the third I 

 have failed to discover, after repeated examination, any- 

 thing abnormal. 



Many lake basins have been ascribed to the erosive 

 action of glaciers. Since the late Sir .A. Ramsay advanced 

 this hypothesis, numbers of lakes in various countries have 

 been carefully investigated and the results published, the 

 most recent of which is the splendid work on the Scottish 

 lochs by Sir J. Murray and Mr. L. Pullar.^ A contribution 

 to science of the highest value, it has also a deeply pathetic 

 interest, for it is a father's memorial to a mucli-loved son, 

 F. P. Pullar, who, after taking a most active part in 

 beginning the investigation, lost his life while saving others 

 from drowning. As the time at my command is limited, 

 and many are acquainted with the literature of the sub- 

 ject, I may be excused from saying more than that even 

 these latest researches have not driven me from the posi- 

 tion which I have maintained from the first, namely, that 

 while many tarns in corries and lakelets in other favour- 

 able situations are probably due to excavation by ice, as 

 in the mountainous districts of Britain, in Scandinavia, 

 or in the higher parts of the .Mps, the difficulty of invoking 

 this agency increases with the size of the basin — as, for 

 example, in the case of Loch .Maree or the Lake of Annecy 

 — until it becomes insuperable. Even if Glas Llyn and 

 Llyn Llydaw were the work of a glacier, the rock basins 

 of Gennesaret and the Dead Sea, still more those of the 

 great lakes in North .America and in Central .Africa, must 

 be assigned to other causes. 



I pass on, therefore, to mention another ditficultv in 

 this hypothesis — that the .Alpine valleys were greatly 

 deepened during the Glacial Epoch — which has not yet, I 

 think, received sufficient attention. From three to four 

 hundred thousand years have elapsed, according to Penck 

 and Bruckner, since the first great advance of the .Alpine 

 ice. One of the latest estimates of the thickness of the 

 several geological formations assigns 4000 feet ' to the 

 Pleistocene and Recent, 13,000 to the Pliocene, and 14,000 

 to the Miocene. If we assume the times of deposit to be 

 proportional to the thickness, and adopt the larger figure 

 for the first-named period, the duration of the Pliocene 

 would be 1,300,000 years, and of the Miocene 1,400,000 

 years. To estimate the total vertical thickness of rock 

 which has been removed from the Alps by denudation is 

 far from easy, but I think 14,000 feet would be a liberal 

 allowance, of which about one-seventh is assigned to the 

 Ice .Age. But during that age, according to a curve given 

 by Penck and Bruckner, the temperature was below its 

 present amount for rather less than half (0-47) the time. 

 Hence it follows that, since the sculpture of the .Alps must 

 have begun at least as far back as the Miocene period, 

 one-seventh of the work has been done by ice in not quite 

 one-fifteenth of the time, or its action must be very potent. 

 .Such data as are at our command make it probable that 



1 If one may judge from photographs, the smoothing of the flanks of ."l 

 valley is unusually conspicuous in Muton .Sound. New Zealand. 



- " Bathvmetrical Survey of the Scottish Freshwater Lochs." Sir I. 

 Murray and Mr. L. Pullar, loio. 



■■ I have doubts whether this is no' too ^reat. 



NO. 2 13 I, VOL. 84] 



a Norway glacier at the present day lowers its basin by 

 only about 80 millimetres in 1000 years; a Greenland 

 glacier may remove some 421 millimetres in the same time, 

 while the Vatnajdkul in Iceland attains to 647 milliinetres. 

 If Alpine glaciers had been as effective as the last-named, 

 they would not have removed, during their 188,000 years 

 of occupation of the .Alpine valleys, more than 121-6 metres, 

 or just over 397 feet ; and as this is not half the amount 

 demanded by the more moderate advocates of erosion, we 

 must either ascribe an abnormal activity to the vanished 

 .Alpine glaciers, or admit that water was much more 

 effective as an excavator. 



We must not forget that glaciers cannot have been 

 important agents in the sculptuie of the Alps during more 

 than part of Pleistocene times. That sculpture probably 

 began in the Oligocene period ; for rather early in the 

 next one the great masses of conglomerate, called 

 Nagclfluh, show that powerful rivers had already carved 

 tor themselves valleys corresponding generally with, and 

 nearly as deep as, those still in existence. Temperature 

 during much of the Miocene period was not less than 

 12° V. above its present average. This would place the 

 snow-line at about 12,000 feet.' In that case, if we 

 assuine the altitudes unchanged, not a snowfield would 

 be left between the Simplon and the Maloja, the glaciers 

 of the Pennines would shrivel into insignificance, Monte 

 Rosa would exchange its drapery of ice for little more 

 than a tippet of frozen snow. As the temperature fell, 

 the white robes would steal down the mountain-sides, the 

 glaciers grow, the torrents be swollen during all the 

 warmer months, and the work of sculpture increase in 

 activity. Yet with a temperature even b° higher than it 

 now is, as it might well be at the beginning of the 

 Pliocene period, the snow-line would be at 10,000 feet ; 

 numbers of glaciers would have disappeared, and those 

 around the Jungfrau and the Finster Aarhorn would be 

 hardly more important than they now are in the Western 

 Oberland. 



But denudation would begin so soon as the ground rose 

 above the sea. Water, which cannot run off the sand 

 exposed by the retreating tide without carving a miniature 

 system of valleys, would never leave the nascent range 

 intact. The Miocene .Alps, even before a patch of snow 

 could remain through the summer months, would be carved 

 into glens and valleys Towards the end of that period 

 the .Alps were affected by a new set of movements, which 

 produced their most marked effects in the northern zone 

 from the Inn to the Durance. The Oberland rose to 

 greater importance ; Mont Blanc attained its primacy ; the 

 massif of Dauphin^ was probably developed. That, and 

 still more the falling temperature, would increase the snow- 

 fields, glaciers, and torrents. The first would be, in the 

 main, protective; the second, locally abrasive; the third, 

 for the greater part of their course, erosive. No sooner 

 had the drainage system been developed on both sides of 

 the .Alps than the valleys on the Italian side (unless we 

 assume a very different distribution of rainfall) would work 

 backwards more rapidly than those on the northern. Cases 

 of trespass, such as that recorded by the long level trough 

 on the north side of the Maloja Kulm and the precipitous 

 descent on the southern, would become frequent. In the 

 Interglacial episodes — three in number, according to Penck 

 and Bruckner, and occupying rather more than half the 

 epoch — the snow and ice would dwindle to something like 

 its present amount, so that the water would resume its 

 work. Thus I think it far more probable that the V-like 

 portions of the -Alpine valleys were in the main excavated 

 during Pliocene ages, their upper and more open parts 

 being largely the results of Miocene and yet earlier 

 sculpture. 



During the great adv.inces of the ice, four in number, 

 according to Penck and Bruckner, " when the Rhone glacier 

 covered the lowlands of A'aud and Geneva, welling on one 

 occasion over the gaps in the Jura, and leaving its erratics 

 in the neighbourhood of Lyons, it ought to have given 



' I take the fall of temperature for a rise in altitude as r° F. for 300 feet 

 or, when the differences in t'le latter are large. 1° per 1000 feet. These esti- 

 m.ites will. I think, be sufficiently accurate. The figures given by Hann(see 

 for a dtsrussion of the question. Report of Urit. Assoc, -1909, p. 93) work 

 out to 1° F. for each 318 feet of ascent (un to about 10,000 feet). 



- On the exact number I have not had the opportunity of forming an 

 opinion. 



