Septembeb 9, 1910] 



SCIENCE 



329 



been as effective as the last-named, they 

 would not have removed, during their 188,- 

 000 years of occupation of the Alpine val- 

 leys, more than 121.6 meters, 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 ab- 

 normal activity to the vanished Alpine 

 glaciers, or admit that water was much 

 more effective as an excavator. 



We must not forget that glaciers can not 

 have been impox'tant agents in the sculp- 

 ture of the Alps during more than part of 

 Pleistocene times. That sculpture prob- 

 ably began in the Oligoeene period; for 

 rather early in the next one the great 

 masses of conglomerate, called Nageliluh, 

 show that powerful rivers had already 

 carved for themselves valleys correspond- 

 ing generally with and nearly as deep as 

 those still in existence. Temperature dur- 

 ing much of the Miocene period was not 

 less than 12° F. above its present average. 

 This would place the snow-line at about 

 12,000 feet.^'^ In that case, if we assume 

 the altitudes unchanged, not a sno^\'field 

 would be left between the Simplon and the 

 jMaloja, 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 glaciei's 

 grow, the torrents be swollen during all the 

 warmer months, and the work of sculpture 

 increase in activity. Yet with a tempera- 

 ture even 6° higher than it now is, as it 

 might well be at the begirming of the Plio- ' 



" I take the fall of temperature for a rise in 

 altitude as 1° F. for 300 feet or, when the differ- 

 ences in the latter are large, 3° per 1,000 feet. 

 These estimates will, I think, be sufficiently accu- 

 rate. The figures given by Hann (see for a dis- 

 cussion of the question, Report of Brit. Assoc, 

 1909, p. 93) work out to 1° F. for each 318 feet 

 of ascent (up to about 10,000 feet). 



cene period, the snow-line would be at 10,- 

 000 feet; numbers of glaciers would have 

 disappeared, and those around the Jung- 

 frau 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 can not run off the sand exposed by 

 the retreating tide without carving a 

 miniature system of valleys, would never 

 leave the nascent range intact. The Mio- 

 cene Alps, even before a patch of snow 

 could remain through the summer months, 

 would be carved into glens and vaUeys. 

 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 pri- 

 macy ; the massif of Dauphine was probably 

 developed. That, and still more the fall- 

 ing temperature, would increase the snow- 

 fields, glaciers and torrents. The first 

 would be, in the main, protective; the sec- 

 ond, locally abrasive; the third, for the 

 greater part of their course, erosive. No 

 sooner had the drainage system been de- 

 veloped on both sides of the Alps than the 

 valleys on the Italian side (unless we as- 

 sume a very different distribution of rain- 

 fall) would work backwards more rapidly 

 than those on the northern. Cases of tres- 

 pass, 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 num- 

 ber, according to Penck and Briiekner, and 

 occupjnng rather more than half the epoch 

 — the snow and ice would dmndle to some- 

 thing like its present amount, so that the 

 water would resume its woi'k. Thus I think 

 it far more probable that the V-like por- 



