402 



CHAPTER XLI. 



mSULAE TLOEAS AND FAUNAS CONSIDEEED Y/ITH EEFEKENCE 



TO THE OKIGIN OF SPECIES. 



VOLCANIC ORIGIN AND MIOCENE AGE OF THE ATLANTIC ISLANDS— ISLANDS 

 ONCE FORMED HAVE NOT BEEN SINCE SUBMERGED, NOR UNITED WITH OTHER 



ARGUMENTS AGAINST CONTINENTAL EXTENSION MAP SHOWING 



ISLANDS 



THE GREAT DEPTH OF THE OCEAN BETWEEN THE VOLCANIC ARCHIPELAGOS 

 OF THE W^ESTERN ATLANTIC AND THE MAINLAND— SUBMARINE VOLCANIC 

 ERUPTIONS OF THE PRESENT CENTURY— GENERAL INFERENCES TO BE DE- 

 DUCED FROM THE ENDEMIC AND OTHER SPECIES OF ANIMALS AND PLANTS 

 IN THE ATLANTIC ISLANDS— FROM MAMMALIA— FROM BIRDS— FROM INSECTS 

 FROM PLANTS— FROM LANDSHELLS — SMALL NUMBER OF SPECIES OF 

 LANDSHELLS COMMON TO MADEIRA AND PORTO SANTO— PROPORTION OF 

 SPECIES COMMON TO MADEIRA AND THE DEZERTAS— CONTRAST OF THE TESTA- 

 CEOUS FAUNA OF THE BRITISH ISLES AND THAT OF THE ATLANTIC ISLANDS 

 MODE IN WHICH AN OCEANIC ISLAND MIGHT BECOME PEOPLED WITH 



LANDSHELLS 



THAN 



CONTINENTS. 



In the present chapter I shall consider the characteristic 

 features of the fanna and flora of islands remote from con- 

 tinents. It has been truly said, that the distribution of 

 species in such peculiar situations affords perhaps the severest 



Natural 



can be tried. 



I have already stated that as a general rule, when islands 

 are near a continent, especially if they are only divided from 

 it by a shallow sea, less, for example, than 100 fathoms m 

 depth, their flora and fauna are identical with that of the 



mainland. 



Mada 



mainland 



miles 



differ from those on the continent, although nearly all^ the 

 genera are the same, while of the other members of the animal 

 and vegetable kingdom there is a greater or less identity 

 according to the class to which they belong. 



If we then go a step farther, and contemplate small islands 



