Vol. 57.] CLIMATE OF THE PLEISTOCENE EPOCH. 441 



Glacial Period, forming then, as now, part of the northern sub- 

 tropical belt of high pressure, the necessary complement of the 

 Equatorial low-pressure trough. 



In any case, the general result is that so long as the north- 

 eastern part of the North Atlantic is prevalently cyclonic,^ so 

 long must southerly and south-westerly winds often occur there, 

 with mild or warm weather over the British Isles. It is only when 

 the influence of such winds is diverted from our shores, and the 

 alignment of the isobars produces northerly or easterl}'' winds, or 

 when Great Britain is anticyclonic, that our winters can be severe. 

 Equally, it seems to me, no great ice-sheet could have originated 

 in Great Britain, and especially in the western part of these 

 islands, while they were under meteorological conditions similar to 

 those now prevalent during winter. 



The effect of winds upon the accumulation or melting of snow is 

 well known. In Siberia, for example, the heat of the sun in spring 

 exerts little or no effect upon it, but when, early in June, warm 

 breezes from the south begin to blow, the ground is cleared of 

 its wintry covering, as if by magic, and heated winds ' eat up ' 

 the snow everywhere.^ Prof. James Geikie says, as showing the 

 infl.uence of winds upon climate, that where the flat lands of the 

 Arctic regions are exposed to the northern blasts, the tundras 

 invade the forest-zone, but where they are sheltered from them, the 

 woods encroach on the tundras, so as nearly to reach the shores of 

 the Polar Sea.^ 



The meteorological conditions which may have been prevalent 

 in summer in the North Atlantic during the maximum glaciation 

 of America, resembling to some extent those now prevalent there 

 in winter, would also have been adverse to the accumulation of 

 an ice-sheet in Great Britain. At present the south-westerly 

 winds caused by the Icelandic cyclone may start in winter from 

 a region as far south as the latitude of the Azores, bringing, even 

 in December and January, air sufficiently warm to produce in 

 this country a maximum temperature of from 55° to 60° Eahr. ; in 

 summer, similar winds are, of course, considerably warmer."* Even 

 in Labrador, and the Hudson Bay region, where the rainfall is as 

 great, and the average winter-temperature as low (from 0° to — 20° 

 Fahr.) as in Greenland, the heat in summer is sufficient to prevent 

 the accumulation of a permanent ice-sheet, and such must equally 

 have been the case in Great Britain, I think, under the conditions 

 just stated. 



The view that the maximum extension of the ice may have taken 

 place at the same time on both sides of the Atlantic, involves the 



^ This must often have been the case during the maximum glaciation of 

 Kortb America. 



■^ See Sir Henry Howorth, 'Glacial Nightmare' vol; ii (1893) p. 389; also 

 A. Eussel Wallace, ' Island Life ' 2nd ed. (1892) p. 140. 



3 Scot. Geogr. Mag. vol. xiv (1898) p. 282. 



* The warmth of such cyclones- is partly due to the latent heat set free by 

 condensation, but this also is distributed by the action of the winds. 



