2G4 



NORMAL QUANTITY OF LAND 



[Ch. XII 



transposition of sea and land in the polar and equatorial 



zones, we 



ought to expect a 



corresponding amount of 

 change in the outline of continents and islands in other 

 regions. This I fully admit ; but those changes might take 

 place without in the least degree affecting the general climate 

 of the globe or the average temperature of the atmosphere. 

 So long as the conversion of sea into land or land into sea 

 does not cause any alteration in the proportions of land to 



same 



t 



ake place without those zones being rendered warmer or 

 colder. Even if the land and sea in the eastern and western 

 hemispheres were to change places, this need not affect the 

 general temperature of the earth's surface, although the 

 transfer of an equal volume of land from the torrid zone to 

 the arctic or antarctic regions would cause a prodigious 

 refrigeration in all latitudes. I have therefore left the land 

 and sea as they now are, that those variations in geography 

 Avhich would affect climate may be more easily recognised. 

 In this same map it will be seen that the diminution of arctic 

 and antarctic land would enable oceanic currents to now more 

 freely from high to low, and from low to high latitudes, so 

 that there might always be much open sea at the poles. 



Mr. Darwin, in one of his interesting speculations on the 

 migration of species in pre- glacial times, has endeavoured to 

 explain the number of plants and animals common to the 

 Old and New World, by supposing that during an earlier and 

 warmer period such as the older Pliocene, there was a con- 

 tinuity of land in high latitudes,* as, for example, between 



North America and North 



It would have been 



easy for me to represent such a state of things in the map 



more than a normal proportion of land to 



without lea vino 



sea within the limits of the arctic circle. I may also ob- 

 serve that the migrations alluded to might have been effected 

 from east to west and from west to east, between the latitudes 



4o and 65 N.. if at SHWASSi'va nArinrls flia rlifFavanf T-»m4s nf 



these continents were each in their turn connected. The 

 hypothesis alluded to does not require that there should have 



* Origin of Species, -1th edition, chap. xi. 





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