Yol. 57.] CLIMATE OF THE PLEISTOCENE EPOCH. 445 



greater extension of the glaciers of the Alps and of the Pyrenees 

 shows that the climate of those regions also, during the maximum 

 glaciation of Europe, must have been considerably colder than it is 

 at present. 



tjnless the southerly winds of the Xorth Atlantic had been 

 diverted from the coasts of Europe, I do not see how the British Isles 

 could have been glaciated. On the other hand, if they had been 

 turned prevalently towards Labrador and I^ew England, the climate 

 of that region, in summer at least, could not have been severe. 



The view that there may have been such a reduction of the heat 

 of tropical regions in Glacial times as to cause the southerly winds 

 of the ISTorth Atlantic to lose their warmth mates, 1 think, a 

 greater demand upon our imagination than does the hypothesis that 

 I have suggested. The facts that the Swiss glaciers did not invade, 

 to any extent, the great plain of Lombardy, and that there is no 

 evidence of extensive glaciation in. the regions bordering the 

 Mediterranean show, however, that the climate of Northern Italy, 

 and generally of the South of Europe, during the Pleistocene Epoch, 

 was not abnormally cold. 



\1. The Meteorological Coin-dittoes duri^^g the Maximum 

 Glaciation of j^orth America. 



Accepting, therefore, as a working hypothesis, the theory that 

 glacial conditions may have been to some extent alternate in the 

 "Western Hemisphere with those of comparative warmth in the 

 Eastern, and conversely, we may now endeavour to ascertain the 

 meteorological conditions which in such a case may have obtained 

 in the former region during the above-named stage of the Pleis- 

 tocene Epoch. 



As before stated, the present winter-climate of Labrador and of 

 the region north-west of Hudson Baj'- (the North American 

 centres of ice-dispersal, according to Prof. Chamberlin) ^ is as severe 

 as that of Greenland. These formerly ice-clad areas lie entirely to 

 the north of the January isotherm of 10° Fahr., while the isotherm 

 of 30° Eahr. for the same month includes nearly all the country 

 supposed to have been covered by the American ice-sheet at the 

 period of its maximum extension (fig. 6, p. 418).^ Such an ice- 

 sheet might therefore exist at the present day, so far as the winter- 

 conditions of iSTorth America are concerned. The summers, however, 

 are hot, almost all the regions supposed to have been ice-clad on the 

 American Continent enjoying in July an average temperature 

 ranging from 50^ to 70° Eahr. (fig. 7, p. 419). The temperature 

 varies widely from day to day in Labrador during summer and 



1 See map in Prof. James Geikie's 'Great Ice Age' 3rd ed. (1894) pi. \iv, 

 facing p. 724. 



-^ Taking the arerage for the whole year, we find that the North American 

 ice-centres of the Pleistocene Epoch lie well to the north of the present isotherm 

 of 30° Fahr. 



2h2 



