Br. Ricketts — On the Cause of the Glacial Period. 579 



With the removal of the Gulf Stream the North Polar Current 

 could have had no higher temperature than that which it derived 

 from the Temperate Zone, thus greatly intensifying the cold, so 

 that the moisture which the atmosphere contained would have been 

 condensed out of it in the form of" snow in much lower latitudes 

 than at present, probably forming a great ice-barrier across the 

 northern extremity of the North Atlantic. With such an extensive 

 field of ice between the Atlantic and Arctic Oceans it is improbable 

 that sufficient water could remain in the atmosphere to admit, 

 within the area of the latter, sufficient precipitation to form ice- 

 floes as extensive, or as thick, as occur there now. 



With the British Isles covered with a great thickness of snow, 

 and with glaciers coming down to the sea, it may be presumed that 

 the southern limits of the ice-drift might have ranged from some- 

 what south of 50° N. to about 60° N. near the longitude of Iceland ; 

 but an extensive frozen area, such as it would have formed, would 

 condense the water contained in the atmosphere, so that, upon the 

 supposition that there exists an open Polar Sea where our Arctic 

 explorers expect to find it, the ice-floe caused by its precipitation 

 could then have hardly extended much farther northward than the 

 latitude of North Cape, the most northern point of Norway, and 

 beyond it there would probably have been an open Polar Ocean. 



Prof. Geikie and Mr. James Geikie have shown that in Scotland 

 there are evidences which demonstrate the occurrence of a succession 

 of Glacial Periods, having intervening times characterized by a mild 

 and even genial climate. These intercalated temperate periods have 

 been considered to be indirectly due to the precession of the 

 Equinoxes, which during a period of extreme eccentricity would 

 gradually have caused the supposed ice-cap to shift from one pole 

 to the other. The occurrence of a succession of depressions and 

 upheavals of Central America, causing communications and separa- 

 tions of the two oceans, would certainly cause the same phenomena 

 to take place, and might not only account for these interposed Glacial 

 Periods, but also for the occurrence of shells having a boreal 

 character during intervals in the Tertiary Period. It is a circum- 

 stance not unlikely to have happened, but of which we have no 

 absolute proof ; nor has any evidence of it been sought for. Tempo- 

 rary upheavals and subsequent depression have been not unfrequent 

 both during the deposit of Palaeozoic as well as more recent forma- 

 tions. 



Mr. P. P. Carpenter has suggested that the intercommunication 

 between the two oceans may have been correlative with the glacial 

 conditions in European seas ; whilst others, and none more clearly 

 than Messrs. Croll and Geikie, have demonstrated how immensely 

 the temperature of the North Atlantic would be diminished by the 

 removal of the Gulf Stream, causing " Scotland to experience a 

 climate as severe as that of Labrador, while the greater part of 

 Norway would be uninhabitable." l 



It has now, I think, been proved that, with the present contour of the 

 1 Mr. James Geikie, " Great Ice Age." 



