The Malay archipelago : the land of the orang-utan ... - Wallace Online

—I114 THE MALAY ARCHIPELAGO. [chap.pairs, and indicating tlie number of species common to each13aii-. Thus:Borneo• • • 29 species Uq species common to both islands,bumatra .'-21 do. J.Borneo. . . 29 do. Uq do. do.Java .... 2/ do. JSumatra . . 21 do.Java. ... 27 do.^^^ ^•^- ^''}Making some allowance for our imperfect knowledge of theSumatran species, we see that Java is more isolated from thetwo larger islands than they are from each other, thus entirelyconfirmingthe results given by the distribution of birds andMammalia, and rendering it almost certain that the last-namedisland was the first to be completely separated from theAsiatic continent, and that the native tradition of its havingbeen recently separated from Sumatra is entirely withoutfoundation.We are now enabled to trace out with some probability thecour.se of events. Beginning at the time when the whole ofthe Java sea, the Gulf of Siam, and the Straits of ]\Ialacca weredry land, forming with Boi'neo, Sumatra, and Java, a vastsouthern prolongation of tlie Asiatic continent, the first movementwould be the sinking down of the Java sea, and the Straitsof Sunda, consequent on the activity of the Javanese volcanoesalong the southern extremity of the land, and leading to thecomiDlete separation of tliat island. As the volcanic belt ofJava and Sumatra increased in activity, more and more of theland was submerged, till first Borneo, and afterwards Sumatra,became entirely severed. Since the epoch of the first disturbance,several distinct elevations and depressions may havetaken place, and the islands may have been more than oncejoined with each other or \nth tlie mainland, and againseparated. Successive waves of immigration may thus havemodified their animal jDroductions, and led to those anomaliesin distribution whicli are so difiicult to account for by any singleoperation of elevation or submergence. The form of Borneo,consisting of radiating mountain chains with intervening broadalluvial valleys, suggests the idea that it has once been muchmore submerged than it is at present (when it would have somewhatresembled Celebes or Gilolo in outline), and has beenincreased to its present dimensions by the filling up of its gulfswith sedimentary matter, assisted by gradual elevation of theland. Sumatra has also been evidently much increased in sizeby the formation of alluvial plains along its north-eastern coasts.There is one peculiarity in the productions of Java that isvery puzzling—the occurrence of several species or groupscharacteristic of the Siamese countries or of India, but whichdo not occur in Borneo or Sumatra. Among Mammals the