492 The Aru Islands. 



insects, which we should imagine could easily cross over. 

 The island of Timor (as I have already shown in Chapter 

 XIII.) bears this relation to Australia; for while it contains 

 several birds and insects of Australian forms, no Australian 

 mammal or reptile is found in it, and a great number of the 

 most abundant and characteristic forms of Australian birds 

 and insects are entirely absent. Conti-ast this with the Brit- 

 ish Islands, in which a large proportion of the plants, insects, 

 reptiles, and Mammalia of the adjacent parts of the Continent 

 are fully represented, while there are no remarkable deficien- 

 cies of extensive groups, such as always occur when there is 

 reason to believe there has been no such connection. The 

 case of Sumatra, Borneo, and Java, and the Asiatic continent 

 is equally clear ; many large Mammalia, terrestrial birds, and 

 reptiles being common to all, while a large number more are 

 of closely allied forms. Now geology has taught us that 

 this representation by allied forms in the same locality implies 

 lapse of time, and we therefore infer that in Great Britain, 

 where almost every species is absolutely identical with those 

 on the Continent, the separation has been very recent ; while 

 in Sumatra and Java, where a considerable number of the 

 continental species are represented by allied forms, the sepa- 

 ration Avas more remote. 



From these examples we may see how important a supple- 

 ment to geological evidence is the study of the geographical 

 distribution of animals and plants, in determining the former 

 condition of the earth's surface ; and how impossible it is to 

 understand the former without taking the latter into account. 

 The productions of the Aru Islands ofier the strongest evi- 

 dence that at no very distant epoch they formed a part of 

 New Guinea ; and the peculiar physical features which I have 

 described, indicate that they must have stood at very nearly 

 the same level then as they do now, having been separated 

 by the subsidence of the great plain which formerly connected 

 tliem with it. 



Persons who have formed the usual ideas of the vegetation 

 of the tropics — who picture to themselves the abundance and 

 brilliancy of the flowers, and the magnificent appearance of 

 liundreds of forest trees covered with masses of colored bios- 



