R. M. Deeley — Polar Climates. 451 



zones at earlier periods of the earth's history. Eckhardt 1 also 

 remarks that the geological contrasts up to the middle of the Cainozoic 

 were not so pronounced as they are now, and it may he said with 

 perfect safety that the climate of the Tertiary and the preceding 

 geological epochs, especially in the Northern Hemisphere, had on 

 wide stretches in the higher latitudes an apparently more insular 

 character with less temperature extremes than the present, above all 

 with warmer winters. Indeed, the late Tertiary earth movements 

 seem to have resulted in a land distribution which caused a radical 

 change in the climates of high latitudes. 



The great uniformity of the forms of life flourishing at the same 

 time in very different latitudes in past ages has greatly simplified 

 the task of the correlation of widely separated rock formations, and 

 what is often regarded as the mingling of boreal, temperate, and 

 tropical forms of life in late Tertiary or Pliocene deposits, as at 

 St. Erth, may be explained by regarding them all as warm temperate 

 forms, the descendants of some of which have survived as temperate, 

 some as tropical, and some as boreal forms, whilst some have become 

 extinct. However, even before Red Crag times there were probably 

 portions of the Arctic Sea cold enough to give rise to boreal forms of 

 mollusca, etc., which spread south as the temperature fell. 



With the causes that may have led at times to the lowering of the 

 temperature of the whole earth I do not purpose to touch upon at all 

 here. My desire is to call attention to certain considerations which 

 may elucidate the difficulties that are met with in the study of Polar 

 climates of past ages as shown by the geological record. Other 

 hypotheses have been brought forward to account for the facts ; but 

 they have not received any general support and would take up too 

 much space to fully discuss here. 



It is agreed that at the present time ocean currents have a very 

 powerful effect upon climate. They carry immense quantities of 

 heat from hot to cooler regions, and warm regions are to some extent 

 cooled by cold Polar currents. But although the heat is mainly 

 carried from latitude to latitude by the water of the ocean, the 

 direction in which the ocean currents travel is dependent upon the 

 direction of the winds. If heat were not carried from latitude to 

 latitude by ocean currents and the winds, the differences of temperature 

 between localities in the same latitude but in different longitudes 

 would be much less marked than they are. Such cold currents as 

 flow from the Polar areas are caused to do so by the winds. If the 

 surface winds travelled wholly towards the Poles the return colder 

 currents would be deep-sea ones. 



Labrador is in the same latitude as England, yet the climates are 

 very different, and the difference is due to the fact that Western 

 Europe enjoys south-westerly winds, especially in the winter, whilst 

 Labrador is chilled by winds from the north. Bouvet Island and the 

 Isle of Man are in practically the same latitude, yet the former is 

 now glaciated down to the sea-level. 



From the point of view of climate the direction in which the winds 



1 Die Wissenschaft, xxxi, Brunswick, 1909. 



