Yol. 57.] THE CLIMATE OP THE PLEISTOCENE EPOCH. 457 



a portion of the Gulf Stream now flowing northward from the 

 Equator may have heeu deflected southward by the agency of winds. 

 Even under such circumstances, I think, an interchange between 

 the Equatorial and Arctic waters must have taken place so long as 

 the channel, 500 miles wide, between Iceland and Great Britain, 

 remained open. Warm currents flowing northward would probably 

 have still hugged the coasts of Europe and have been accompanied, 

 as now, by the frequent recurrence of cyclonic conditions and mild 

 winds in winter over the British Isles, the currents and the winds 

 acting and re-acting on each other.^ It appears necessary, therefore, 

 to suppose that the Icelando-British Channel must have been closed," 

 either by some elevation of the submarine ridge which stretches, 

 although not continuously, from Iceland to Great Britain, or by ice, 

 or possibly by both causes combined, before a permanent ice-sheet 

 could have accumulated in Great Britain.^ There does not seem 

 anything intrinsically improbable in this view ; indeed, there is 

 evidence to show that such may formerly have been the case. 

 Danish naturalists believe that at some stage during the Glacial 

 Period the depth of the sea between Norway and Iceland was much 

 less than it is at present, the dead shells of shallow-water forms 

 of Arctic mollusca having been dredged there in great abundance 

 from a considerable depth. An elevation of 2000 feet would have 

 created a land-communication between Greenland and Great Britain, 

 while one of half that amount would have restricted the communi- 

 cation between the two seas to a few comparatively narrow channels 

 of moderate depth ^ ; these, under such circumstances, might have 

 become wholly or partly blocked by the grounding of icebergs, 

 which can only float in deep water, nine-tenths of their volume 

 being necessarily submerged.^ 



If, however, the Greenland o- British Channel had been closed at 

 that period, a condition of things would have arisen similar to that 

 now existing in the Polar Sea north of Behring Strait.^ The 

 influx of warm water from the Atlantic having been cut off, the 

 region to the north of the Greenlando-British ridge would have 

 become anticyclonic. The south-westerly winds (the influence of 



^ It seems impossible in these matters to distinguish between cause and effect. 

 Temperature, pressure, winds, and oceanic currents act and re-act on each other 

 as links in an endless chain. 



^ Warm currents from the Atlantic enter the Polar basin to the east only of 

 Iceland. 



^ An additional argument in favour of this view will be found on p. 464. 



•* These channels may have been deepened by the scour of currents since the 

 commencement of the Glacial Period. If communication between the Polar 

 Sea and the Atlantic has been cut off and again gradually reopened, this seems 

 more than probable. 



^ Croll estimated that the submerged portion of an iceberg to that above 

 israter is as 8'7 : 1 ; see ' Climate & Time ' 1875, p. 384. 



•^ Behring Strait is about 36 miles wide at one point, but for the most part con- 

 sidel-ably more ; the amount of water entering the Polar Sea through the strait 

 is not sufficient to influence, either directly or indirectly, the winter-chmate of 

 the adjoining regions. 



