ORIGIN OF ISLANDS. 



229 



extremely numerous, can be brought into closer union 

 and reduced to the smallest number possible, as by our 

 theory the Mammalia have but one point of derivation, 

 and if we can herewith harmonize the geological succes- 

 sion of the organisms examined, or, in other words, 

 harmonize the horizontal distribution with the vertical 

 or historical sequence, animal geography will then ap- 

 proach the solution of its task. Wallace and Rtitimeyer's 

 works are therefore an important advance, as the former 

 has given detailed evidence that the fauna of the com- 

 plex and extensive Australio-Indian Archipelago is by 

 no means self-dependent, but consists merely of off- 

 shoots of the continents; and the latter, in a grand sur- 

 vey of the entire surface of the earth, has reduced the 

 centres of distribution to the simplest proportions as yet 

 possible. 



The comparison of insular and continental faunas is 

 naturally of great interest. For should it appear that, 

 with respect to the animal world, islands are one and all 

 mere appendages of the continents, the problem would 

 at once be vastly simplified. If we follow Peschel's 

 luminous exposition of the origin of islands,'^ we have 

 first to deal with the fragments of continents. A great 

 number of islands, such as Great Britain and the great 

 Asiatic islands, may be recognized at once as fragments 

 of still existing continents. On the other hand, Mada- 

 gascar and the Seychelles are not, as might be con- 

 jectured, a segment of Africa, but the remnant of a 

 former continent very peculiar in its flora and fauna. 

 Other islands originate either from submarine volcanoes 

 or from corals, and in the latter case the structure is 

 founded on sinking land. It naturally follows that on 



