THE DISTRIBUTION OF ANIMALS AND PLANTS 405 



those migrations, extinctions, and renovations of which their 

 fossil remains and present distribution afford evidence. 



Still, it is true that throughout the whole of these great 

 mutations, since the beginning of geological history, there 

 seems never to have been any time when the ocean so regained 

 its dominion as to produce a total extinction of land life ; 

 still less was there any time when the necessary conditions of 

 all the various forms of marine life failed to be found ; nor 

 was there any climatal change so extreme as to banish any 

 of the leading forms of life from the earth. To geologists it is 

 not necessary to say that the conclusions sketched above are 

 those that have been reached as the results of long and 

 laborious investigation, and which have been illustrated and 

 established by Lyell, Dana, Wallace,^ and many other writers. ^ 

 Let us now place beside them some facts as to the present 

 distribution of hfe, and of tlie agencies which influence it. 



Just as political geography sometimes presents boundaries 

 not in accordance with the physical structure of countries, so 

 the distribution of animals and plants shows many peculiar 

 and unexpected features. Hence naturalists have divided the 

 continents into what Sclater has called zoological regions, 

 which are, so to speak, the great empires of animal life, divisible 

 often by less prominent boundaries into provinces. In vege- 

 table life similar boundaries may be drawn, more or less coin- 

 cident with the zoological divisions. Zoologically, North 

 America and Greenland may be regarded as one great region, 

 the Nearctic, or new Arctic, the prefix not indicating that the 

 animals are newer than those of the old world, which is by no 

 means the case. South America constitutes another region — 



^ Wallace, "Geographical Distribution of Animals" and "Island Life." 

 Second edition. 



2 The writer has endeavoured to popularize these great results of geology 

 in his work, the "Story of the Earth." Ninth Edition. London, 1887. 

 They are often overlooked by specialists, and by compilers of geological 

 manuals. 



