Vol. 57.] CLIMATE OF THE PLEISTOCENE EPOCH. 467 



continental land-tract, the eastern margin of which is supposed to 

 have lain to the north-east of the West Indies, as shown by a 

 dotted line in fig. 21 (p. 458), would seem to have existed at 

 some stage of the Glacial Period over what is now the Gulf of 

 Mexico. This region, under the influence of the vertical rays 

 of the sun in summer, must have been then very hot (with an 

 average temperature of possibly 80° Fahr.), and would therefore 

 have been cyclonic, instead of anticyclonic at that season as at 

 present. But such conditions would have caused a prevalence 

 of heated south-easterly winds , over the southern part of the 

 United States, as shown in fig. 22 (p. 460), which would have 

 rendered the existence of an ice-sheet in ]N"orth America as far 

 south as lat. 37° 35' N. (its supposed maximum extension) 

 impossible. 



Let it be assumed that a gradual elevation of the Antillean region 

 coincided with subsidence in Labrador, the IN^orth American 

 continent having moved from south to north as on a pivot, as did 

 the Anglo-Belgian Basin in Pliocene and Pleistocene times : ice 

 would then have accumulated more slowly in the north, while, at 

 the same time, it would have been melted back in the south. If, 

 further, the depression of Labrador had been contemporaneous with 

 an elevation of Scandinavia and the British Isles, ^ and especially 

 of the Icelando-British ridge, an ice-sheet might have begun to 

 form on the Scandinavian highlands, coincidently with the shrinking 

 of the' ice in North America. In the struggle between the 

 anticyclones of the Old and New Worlds, similar to that which goes 

 on during the winter at the present day, but attended with 

 more permanent results, the anticyclone of the Eastern Continent 

 might thus have gained the ascendency, and the statistical align- 

 ment of the low-pressure system of the Atlantic might have been 

 altered from south-west and north-east to north-west and south- 

 east, changing the prevalent direction of the warmer winds, 

 and diverting them, together with the oceanic surface-currents, 

 from the coasts of Europe to those of America. Under such 

 circumstances, the ice-sheets of Eastern North America might 

 have gradually diminished, and have finally disappeared, while 

 at the same time glacial conditions established themselves in 

 Europe. 



The fact that the cyclonic system of the North Atlantic, just 

 referred to, now maintains statistically a south-westerly and north- 

 easterly alignment, causing the prevalence of winters comparatively 

 mild in Great Britain, and severe in Labrador, seems to indicate that 

 the influence of the North American anticyclone, other things being 

 equal, may always have been stronger than that of Europe. This 

 being so, the former might have been able after a time, assisted 



. ^ Prof. Bonney believes that au uplift of Great Britain and Scandinavia 

 would have been necessary, in order to make the existence of au ice-sheet 

 possible in those countries ; see ' Ice-Work' 1896, p. 277. Dr. A. R. Wallace 

 argues also, that high land is necessary fur the initiation of a glacial period, 

 ' Island Life' 2nd ed. (1892) p. 1^4. 



