Vol. 57.] CLliTATE or THE PLEISTOCENE EPOCH. 471 



existed, may have coincided with successive alternations in the 

 alignment of the isobars, caused bj' the advance or retreat of the 

 American ice-sheet, originating at one time moist oceanic, and 

 at another dry winds from the land, over the region in question. 



It is difficu.lt, however, to restore h5^pothetically the meteoro- 

 logical conditions of the Pleistocene Epoch, on the theory that the 

 maximum glaciation of the Eastern and Western Continents was 

 contemporaneous. At present the influence of the Gulf Stream and 

 the south-westerly winds indirectly caused bj^ it carries a compara- 

 tively warm climate northward during the winter over the British 

 Isles and Scandinavia into the Polar Circle, but no permanent 

 ice-sheet could have existed in those countries under such circum- 

 stances. The view that the maximum glaciation of I^orth America 

 and Europe was contemporaneous, involves the admission that an 

 enormous anticyclone extended more or less prevalently at that 

 epoch from the Pole southward over a considerable portion of both 

 continents at the same time, during the winter, and to some extent 

 in summer. Such a state of things, however, if even it could have 

 been for a time established, would have been meteorologically of a 

 most unstable character, tending to produce at all seasons atmo- 

 spheric disturbance in the Atlantic, with prevalent southerly and 

 south-westerly winds to the east of the cyclonic centres, flooding 

 North-western Europe with warmth. Conditions similar to those 

 which may have prevailed during the maximum glaciation of 

 North America occurred during the winter of 1898-99, when the 

 weather was persistently and excessively cold in America, and 

 abnormally warm in Europe; temperatures of —60° Fahr. were 

 recorded on the same daj^ in the one, and 70*5° Fahr. in the other ; 

 the former being due to cold winds from the Polar regions, and the 

 latter to warm winds from the subtropical zone, strictly comple- 

 mentary to them, and due to the same cause. 



The northerly winds on the one side, either of a cyclonic or an 

 anticyclonic centre, are the necessary equivalent of the southerly 

 winds on the other. It is not possible, therefore, that the Northern 

 Hemisphere could have been wholly cold at one stage of the Glacial 

 Period, or wholly mild at another. The alignment of the isotherms 

 and the distribution of climatic zones was probably at least as 

 irregular then as at present, arctic and temperate conditions co- 

 existing in difl'erent areas at the same latitude. Indeed, if the 

 disturbances of the atmospheric equilibrium in temperate regions 

 were more marked at that period, as seems probable, the contrasts 

 in climate may have then been even greater than they are now. 



No such meteorological difficulties arise if we adopt the hypo- 

 thesis that the more important Glacial and Interglacial variations 

 of climate may have alternated in the Western and Eastern 

 Continents. Minor changes, however, may have been of more local 

 distribution. 



The winter-temperature of Labrador (one of the North American 

 centres of ice- accumulation during the Glacial Period) is as cold, 

 and the annual rainfall as great, as in Greenland at the present day ; 



