CHAPTER XIX. 



THE CAUSE OF THE GLACIAL PERIOD CONTINUED. 



The eighth theory, which would attribute the growth and 

 disappearance of glaciers entirely to changes in the distribu- 

 tion of land and water over the surface of the globe, was, 

 according to his general principles, ably and ardently advo- 

 cated by Sir Charles Lyell; and no one can read in his 

 " Principles of Geology' ' the chapters upon this subject 

 without being greatly impressed by the possible influences of 

 such changes. The ocean is the great equalizer of the earth's 

 temperature. Through unimpeded ocean-currents, like the 

 Gulf Stream of the Altantic and the Kuro-Siwa cf the Pacific, 

 the heat of the tropics is transferred many thousands of miles 

 to ameliorate the climate of even the polar regions. It is 

 quite possible that comparatively slight changes in level in 

 the vicinity of the West India Islands and Central America 

 might so affect the direction of the Gulf Stream as to produce 

 most serious modifications of the climate in North America 

 and Europe. Should a portion of the Gulf Stream be driven 

 through a depression across the Isthmus of Panama into the 

 Pacific, and an equal portion be diverted from the Atlantic 

 coast of the United States by an elevation of the sea-bottom 

 between Florida and Cuba, the consequences would neces- 

 sarily be incalculably great, so that the mere existence of such 

 a possible cause for great changes in the distribution of moist- 

 ure over the northern hemisphere is sufficient to make one 

 hesitate before committing himself unreservedly to any other 

 theory — at any rate, to one which has not for itself indepen- 

 dent and adequate proof. 



