230 NATURAL HISTORY OF THE [chap. ix. 



to Borneo and one to Sumatra. The isolation of Java will, 

 however, be best shown by grouping the islands in pairs, 

 and indicating the number of species common to each pair. 

 Thus :— 



Borneo . 



Sumatra 

 Borneo . 

 Java . 

 Sumatra 

 Java . 



29 species ) 



9 , , [■ 20 species common to both islands. 



29 do. ) 



27 do. J 20 d0 - d0 - 



21 do. ) 



27 do. i 11 d0 - d0 - 



Making some allowance for our imperfect knowledge of 

 the Sumatran species, we see that Java is more isolated 

 from the two larger islands than they are from each other, 

 thus entirely confirming the results given by the distri- 

 bution of birds and Mammalia, and rendering it almost 

 certain that the last-named island was the first to be com- 

 pletely separated from the Asiatic continent, and that the 

 native tradition of its having been recently separated from 

 Sumatra is entirely without foundation. 



We are now enabled to trace out with some probability 

 the course of events. Beginning at the time when 

 the whole of the Java sea, the Gulf of Siam, and the 

 Straits of Malacca were dry land, forming with Borneo, 

 Sumatra, and Java, a vast southern prolongation of the 

 Asiatic continent, the first movement would be the sink- 

 ing down of the Java sea, and the Straits of Sunda, con- 



