22 president's address. 



opposite direction. 1 But though these changes might diminish the 

 difference between the temperatures of London and Leipzig, they would 

 not make the former colder than the latter. At the present day the 

 snow-line in the Alps on either side of the Upper Ehone Valley is not 

 far irom 8,000 feet above sea-level, and this corresponds with -a tem- 

 perature of about 30°. Glaciers, however, are not generally formed 

 till about 1,000 feet higher, where the temperature is approximately 

 27°. Penck and Bruckner place this line during the coldest part of the 

 Ice Age at about 4,000 feet. 2 In that case the temperature of the Swiss 

 lowland would be some 15° lower than now, or near the freezing-point. 3 

 If this fall were general, it would bring back the small glaciers on the 

 Gran Sasso d 'Italia and Monte Rotondo in Corsica; perhaps also among 

 the higher parts of the Vosges and Schwarzwald. 4 In our own country it 

 would give a temperature of about 35° at Carnarvon and 23° on the top 

 of Snowdon, of 32° at Fort William and 17°. 5 on the top of Ben Nevis. 

 If : in addition to this, the land were 600 feet higher than now (as it 

 probably was, at any rate in the beginning of the Glacial Epoch), there 

 would be a further drop of 2°, so that glaciers would form in the corries 

 of Snowdon, and the region round Ben Nevis might resemble the 

 Oetzthal Alps at the present day. This change of itself would be in- 

 sufficient, and any larger drop in the ocean-level would have to be con- 

 tinental in its effects, since we cannot assume a local upheaval of much 

 more than the above amount without seriously interfering with the 

 river system of North Central Europe. But these changes, especially 

 the former, might indirectly diminish the abnormal warmth of winter 

 on our north-western coasts. 8 It is difficult to estimate the effect of 

 this. If it did no more than place Carnarvon on the isotherm 

 of Berlin (now lower by 2°), that would hardly bring a glacier 

 from the Snowdonian region down to the sea. At the present time 

 London is about 18° warmer than a place in the same latitude near the 

 Labrador coast or the mouth of the Amur Eiver, but the removal of that 

 difference would involve greater changes in the distribution of sea and 

 land than seems possible at an epoch comparatively speaking so recent. 



1 Facts relating to this subject will be found in Climate and Time, by J. Croll, 

 ch. ii. and iii. (1875). Of course the air currents would also be affected, and perhaps 

 diminish precipitation as the latitude increased. 



2 Loc. cit., p. 586, et seq. They say the snow-line, which would mean that the 

 temperature was only 12° lower than now ; but as possibly this line might then more 

 nearly correspond with that of glacier formation, I will provisionally accept the higher 

 figures, especially since Corsica, the Apennines, and some other localities in Europe, 

 seem to require a reduction of rather more than 12°. 



3 It would be 32°.5 at Zurich, 31°.6 at Bern, 34°.l at Geneva, about 39°.0 on the 

 plain of Piedmont, and 36°. at Lyons. 



4 See for particulars the author's Ice Work (' International Scientific Series '), p. 237. 



5 For much valuable information on these questions see a paper on the Climate of 

 the Pleistocene Epoch (F. W. Harmer, Quart. Journ. Geo!. Soc, lvii. (1901), p. 405). 



