10 ISLAND LIFE 



and then, by a critical examination of their possible causes, 

 to ascertain whether they were isolated phenomena, were 

 due to recurrent cosmical actions, or were the result of a 

 great system of terrestrial development. The latter is the 

 conclusion we arrive at ; and this conclusion brings with 

 it the conviction, that in the theory which accounts for 

 both glacial ej)Ochs and warm polar climates, we have the 

 key to explain and harmonize many of the most anom- 

 alous biological and geological phenomena, and one which 

 is especially valuable for the light it throws on the dis- 

 persal and existing distribution of organisms. The other 

 important theory, or rather corollary from the preceding- 

 theory — that of the permanence of oceans and the general 

 stability of sontinents throughout all geological time, is 

 as yet very imperfectly understood, and seems, in fact, to 

 many persons in the nature of a paradox. The evidence 

 for it, however, appears to me to be conclusive ; and it is 

 certainly the most fundamental question in regard to the 

 subject we have to deal with : since, if we once admit that 

 continents and oceans may have changed i:)laces over and 

 over again (as many writers maintain), we lose all power 

 of reasonino: on the mis^rations of ancestral forms of life, 

 and are at the mercy of every wild theorist who chooses to 

 imagine the former existence of a now-submerged contin- 

 ent to explain the existing distribution of a group of frogs 

 or a genus of beetles. 



As already shown by the illustrative examples adduced 

 in this chajDter, some of the most remarkable and inter- 

 esting facts in the distribution and affinities of organic 

 forms are j)resented by islands in relation to each other 

 and to the surrounding continents. The study of the 

 productions of the Galapagos — so peculiar, and yet so 

 decidedly related to the American continent — aj)pears to 

 have had a powerful influence in determining the direction 

 of Mr. Darwin's researches into the origin of species ; and 

 every naturalist who studies them has always been struck 

 by the unexpected relations or singular anomalies whicli 

 are so often found to characterize the fauna and flora of 

 islands. Yet their full importance in connection with the 

 history of the earth and its inhabitants has hardly yet 



