158 Natural History of the 



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 sinking down of the Java sea and 

 the Straits of Sunda, consequent on the activity of the Java- 

 nese volcanoes along the southern extremity of the land, and 

 leading to the complete separation of that island. As the vol- 

 canic belt of Java and Sumatra increased in activity, more and 

 more of the land was submerged, till first Borneo, and after- 

 ward Sumatra, became entirely severed. Since the epoch of 

 the first disturbance, several distinct elevations and depres- 

 sions may have taken place, and the islands may have been 

 more than once joined with each other or with the main-land, 

 and again separated. Successive waves of immigration may 

 thus have modified their animal productions, and led to those 

 anomalies in distribution which are so difiicult to account for 

 by any single operation of elevation or submergence. The 

 form of Borneo, consisting of radiating mountain chains with 

 intei'vening broad alluvial valleys, suggests the idea that it 

 has once been much more submerged than it is at pi*esent 

 (when it would have somewhat resembled Celebes or Gilolo 

 in outline), and has been increased to its present dimensions 

 by the filling up of its gulfs with sedimentary matter, assist- 

 ed by gradual elevation of the land. Sumatra has also been 

 evidently much increased in size by the formation of alluvial 

 plains along its north-eastern coasts. 



There is one iDeculiarity in the productions of Java that is 

 very puzzling — the occurrence of several sjDCcies or groups 

 characteristic of the Siamese countries or of India, but which 

 do not occur in Borneo or Sumatra. Among mammals the 

 Rhinoceros javanicus is the most striking example, for a dis- 

 tinct species is found in Borneo and Sumatra, while the Jav- 

 anese species occurs in Birmah and even in Bengal. Among 

 birds, the small ground-dove (Geopelia striata) and the curi- 

 ous bronze-colored magpie (Crypsii'hina varians) are common 

 to Java and Siam ; while there are in Java species of Pteruthi- 

 us, Arrenga, Myiophonus, Zoothera, Sturnopastor, and Estrel- 

 da, the nearest allies of which are found in various parts of 

 India, while nothing like them is known to inhabit Borneo or 

 Sumatra. 



