420 ME. F. W. HAEMER ON THE [Aug. IQOI, 



and the climatic zones of the Northern Hemisphere must have 

 caused increased atmospheric disturbance, so that storms would 

 then have been more frequent and more violent ; productive 

 therefore, locally, of a more copious rainfall. 



The present distribution of climatal zones in the J^orthern 

 Hemisphere is very irregular, especially in winter, and a reference 

 to figs. 6 & 7 (pp. 418 tfe 419), the statistical isothermal charts for 

 January and July, will show that important deflexions of the iso- 

 thermal lines from the normal coincide, as a rule, with the direction 

 of the prevalent winds. Whatever may have been the case at 

 more remote epochs, it is not probable that the alignment of the 

 isotherms corresponded more nearly with the parallels of latitude 

 during the Pleistocene Epoch than it does now. If at that 

 time the Equatorial regions were hotter than those of the poles, 

 there would have been a constant interchange between the 

 heated air of the one and the cold air of the other. Moreover, 

 the northerly winds and the southerly winds must always have 

 directly or indirectly balanced each other. When the horizontal 

 circulation of the atmosphere takes place round an area either of 

 low or of high pressure (as for example in fig. 12, p. 439), the cold 

 weather on the one side of the baric centre is the necessary complement 

 of the warm weather on the other. The difference in the arrange- 

 ment of the isobars during the Pleistocene Epoch, involving changes 

 in the direction of the prevalent winds, would, however, have caused 

 variations in climate of a more or less permanent character, 

 widely differing from those of the present day. Oceanic winds 

 with copious rainfall may have then prevailed in regions now arid, 

 and mild winters where they are now excessively severe. 



In illustration of this view it will be sufficient to point to one or 

 two well-known cases of anomalous climate during the Pleistocene 

 Epoch. 



II. The Htjmid Condition's oe the Sahaea dtjeing the 

 Pleistocene Epoch. 



It has long been known that the Great Saharan Desert, now 

 rainless, formerly enjoyed, probably during some part of the 

 Pleistocene Epoch, a comparatively humid climate. No rain falls 

 there now, because at all times of the year the winds blow towards 

 it either from the land, or from the north, and not from the ocean. 

 In other parts of Africa, and in some tropical or subtropical regions, 

 on the contrary, as in India for example, rainy and dry seasons are 

 alternate. In the latter country, the winds blow from the land 

 during the winter months, as pressure is then highest towards 

 the north. In summer, however, the barometric conditions are 

 reversed, causing a strong indraught of south-easterly winds from 

 the Arabian Sea, and where they prevail, the country is deluged 

 with rain. 



Similarly, the humid conditions formerly existing in the North 

 of Africa could only have arisen from the prevalence of westerly or 



