180 SPARKS FROM A GEOLOGIST'S HAMMER. 



in the position of the pole must accompany a change in 

 the position of the compressed and protuberant regions of 

 the earth. This would change to a great extent the rela- 

 tive location of water and land areas. But the strati- 

 fied rocks demonstrate that no considerable changes of 

 this kind have taken place since Silurian Time. And 

 finally, the indications of both warmer and colder climates 

 exist on opposite sides of the polar zone; but a change 

 in the position of the pole, while conferring a milder 

 temperature on one side, say the American Arctic archi- 

 pelago, would bring a sevei'er climate to the opposite 

 side, say in Nova Zembla and Bear Island. 



Again, it was suggested by Poisson,* and maintained 

 by the elder Agassiz, f that perhaps the earth, in the 

 journey of our system through space, passes occasionally 

 through regions of excessive cold. Others have suggested 

 a diminution of the sun's heat, but restored again in later 

 times. % Both suppositions imply that all parts of the 

 earth's surface suffer a depression of temperature at the 

 same time. This would require that traces of glacier 

 action should exist in tropical as well as temperate regions. 

 The facts, in spite of Agassiz' supposed moraines in the 

 empire of Brazil, do not answer to the expectation. 



A theory which enjoys considerable popularity supposes 

 that such distributions of land and water have existed in 

 former times as would change the location of ocean cur- 

 rents to an extent which would revolutionize terrestrial 

 climates. That profound climatic characteristics of cer- 



* Tlieorle math, de la chaletir. Comptes Rendus, Jan. 30, 1837. 



t L. Agassiz, A Journey In Brazil, 399 425. 



t Lyell, Prin. Geol. 128; Sir John Herschel, Proc. Roy. Astron. Soc., No. iii, 

 Jan. 1840. 



Lyell, Principles of Geol., ch. vii, viii; J. W. Dawson, Princeton Review, 

 March 1879; A. R. Wallace, Island Life; Nature,xs\u, 124. 



