TIIK 1M.KISTOCENE SKI; IKS 649 



which would alter the course of the Gulf Stream, but all these 

 ideas are unproved hypotheses. 



The alteration of meteorological conditions as a cause of 

 climatal change has recently been discussed by Mr. F. W. Manner, 29 

 \vlio points out that the winds are an important factor in determin- 

 ing the distribution of climatal zones, and that existing deviations 

 of the monthly or yearly isotherms from the normal are coincident 

 irriierally with the direction of the prevalent winds. " The winds 

 blow in a direction more or less parallel to the isobars ; the latter 

 group themselves round centres of high and low pressure. . . . 

 Anomalous weather is due to some unusual arrangement of these 

 areas ; similarly former cases of anomalous climate can only have 

 occurred when meteorological conditions were favourable. 



" During the Glacial period the regions covered by ice might 

 have been, to a greater or less extent, anticyclonic at all seasons, 

 low-pressure systems prevailing at the same time over the warmer 

 regions immediately to the south of them and over the adjoining 

 oceans. The relative positions of areas of high and low barometric 

 pressure, the direction of the prevalent winds, and the consequent 

 distribution of climatic /ones would in such a case have differed 

 from those of the present time." 



The prevalence of south-westerly winds over the British area at 

 the present time is due to the fact that the centres of cyclonic 

 storms generally pass from the Atlantic to the north or north-west 

 of our islands. Under the conditions above imagined they would 

 pass farther to the south, bringing oceanic winds over the Sahara 

 and the Mediterranean Sea, while easterly winds would prevail 

 over Britain. It has already been mentioned that the shell-banks 

 of the Suffolk and Norfolk Crags afford actual evidence of such 

 easterly winds during the later part of the Pliocene period. 

 Further, as Mr. Harmer points out, " the diversion of the prevalent 

 winds of the northern part of the north Atlantic from a south- 

 w.-sterly to a south-easterly direction would have tended to divert 

 the Gulf Stream, or what remained of it, towards the American 

 coast" This abstraction of the Gulf Stream would have an 

 enormous effect on the climate of Western Europe, equivalent, 

 according to Dr. Croll, to a lowering of the mean annual temperature 

 of London by 40 F. 



With regard to the actual difference in the climate of Northern 

 Europe at the time of the greatest extension of the ice, Mr. C. Reid 

 has estimated that the average temperature of the air along the 

 southern margin of the ice -sheet was not higher than freezing 

 point, and that the mean annual isotherm of 38 F. must then 

 have passed through the south of England and across Central 



