^558 ^W^^ ^^^^^ ISLJNM. [chap, xixul 



same results. The hiittertlies of Aru are all either New 

 Guinea species, or verj slightly modified forms ; whereas 

 those of Ceram are more diatiuct tlian are the birds of the 

 two countries. 



It is BOW generally admitted that we may safely reason 

 on such facts as these, which supply a link in the defective 

 geological record. The upward and downward movements 

 which any comitry has undergone, and tlie succession of 

 such movements, Ciin be determined with much accuracy ; 

 but geology alone can tell us nothing of lands which have 

 entirely disappeared beneath the ocean. Here physical 

 geography and the distribution of animals and plants are 

 of the greatest service. By ascertaining the depth of the 

 seas separating one country from another, we can form 

 some judgment of the change-'s which are taking place. If 

 there are other evidences of subsidence, a shallow sea 

 implies a former connexion of the adjacent lands ; but if 

 this ev idence is wanting, or if there is reason to suspect a 

 rising of the land, then the shallow sea may be the result 

 of that rising, and may indicate that the two countries will 

 be joined at some future time, but not that they have 

 previously been so, The nature of the animals aud plants 

 iiahahiting these countries will, however, ahnost always 

 enable us to determine this {question. Mr. Darwin has 

 shown us how we may determine in almost every case, 

 whether an island has ever been connected with a con- 

 tinent or larger land, by the presence or absence of terres- 

 trial Mamnmlia and reptiles. What he terms " oceanic 

 islands" possess neither of these gi'oups of animals, though 

 they may have a luxuriant vegetation, and a fair nnmber of 

 birds, insects, and land-shelli} ; and we therefore conclude 

 that they have originated in mid-ocean, and have never 

 been eounected with the nearest masses of land St 

 Helena, Madeira, and New Zealand are examples of 

 oceanic islands. They possess all other classes of life, 

 because tliese have means of dispersion over wide spaces 

 of sea, which terrestrial mammals aud birds have not, as 

 is fully explained in Sir Charles Lycll's "Principles of 

 Geology," and Mr. Darwin's Origin of Species." On the 

 other hand, an island may never have been actually con- 

 nected with the adjacent continents or islands, and yet 



