Vol. 57.] CLIMATE OF THE PLEISTOCE^TE EPOCH. 449 



415), as such maps are out of scale for the Polar regions, and do not 

 represent so clearly what I consider may have been the movements 

 of the Arctic high-pressure system during the different phases of 

 the Glacial Period. 



It is the oscillation of the centre of this high-pressure system from 

 one side of the Polar Circle to the other during the Glacial Period, 

 changing, as I think it would have done, the statistical alignment of 

 the low-pressure system of the N^orth Atlantic and the direction of 

 the prevalent storm-tracks, which may have to some extent caused, 

 or have bespn at least coincident with the climatal changes, both 

 of Europe ajnd America. 



In constlrvcting these hj^pothetical diagrams I have repro- 

 duced as far as possible the present meteorological conditions, 

 with such alterations only as the former existence of the ice-sheets 

 may obviously have required. I have given the different isobars in 

 full, as in the statistical charts (figs. 17 & 19, pp. 450 & 454), for 

 purposes of comparison only, and because the task of doing so proved 

 a useful check on the work. I do not suppose for a moment that 

 it can be possible to restore in such detail the meteorology of the 

 Glacial Period. 



Dealing first with the baric conditions of winter, during the 

 maximum glaciation of I^orth America, and comparing figs. 17 & 18 

 (pp. 450 & 452), we may assume that the greater part of the 

 Eurasiatic continent was then, as now at that season, an area 

 of high pressure, Central Asia having been probably at least as 

 cold during the Pleistocene Epoch as it is at present. As to 

 America, I have drawn the central part of the anticyclone of that 

 continent (fig. 18) to coincide roughly with what is supposed to 

 have been the greatest southward extension of the ice,*^ and to 

 include Greenland^ and a part of the Polar Ocean, then perhaps 

 permanently frozen over.^ 



Not only would the actual position and form of this high-pressure 

 system have varied from day to day, however, but it might have been 

 subject also to secular oscillations, and have sometimes extended as 

 far as the northern coasts of Scandinavia. Moreover, every change 



^ See T. 0. Chamberlin's map in Geikie's ' Great Ice Age ' 3rd ed. (1894) 

 pi. xiv, facing p. 724. It is probable, however, that the anticyclones may not have 

 corresponded so symmetrically vrith the limits of the great ice-sheets as shown 

 on my charts ; but I do not know how otherwise to represent the general relation 

 of the former to the latter. 



^ Grreenland may have been during the Glacial Period the pivot, so to speak, 

 upon which the climatal conditions of the Atlantic basin moved, as is the 

 case at present. Wliile the land-tracts, both east and west of it, are now subject 

 to constant changes, the condition of Greenland remains the same, not only at 

 all seasons, but from year to year. It will be seen from my hypothetical charts 

 that on the view taken by me, the winds blowing towards Grreenland would 

 , have come from a cold quarter during the maximum glaciation both of North 

 America and Europe. 



^ It seems doubtful whether the ice-sheet of Greenland was ever confluent 

 with that of North America ; Davis Strait, however, may have been at this 

 period more or less permanently blocked with ice. 



