178 MR. A. R. WALLACE ON THE ZOOLOGICAL 



now siirrouucliiig it, and obtained some part of its fauna before 

 they came into existence. They point to the time wlien a great 

 continent occupied a portion at least of what is now the Indian 

 Ocean, of which tlie islands of Mauritius, Bourbon, &c. may be 

 fragments, while the Chagos Bank and the Keeling Atolls indicate 

 its former extension eastward to the vicinity of what is now the 

 Malayan Archipelago. The Celebes group remains the last eastern 

 fragment of this now submerged land, or of some of its adjacent 

 islands, indicating its peculiar origin by its zoological isolation, 

 and by still retaining a marked affinity with the African fauna. 



The great Pacific continent, of which Australia and New Gruiuea 

 are no doubt fragments, probably existed at a much earlier period, 

 and extended as far westward as the Moluccas. The extension of 

 Asia as far to the south and east as the Straits of Macassar and 

 Lombock must have occiuTcd subsequent to the submergence of 

 both these great southern continents ; and the breaking up and 

 separation of the islands of Sumatra, Java, and Bdrneo has been 

 the last great geological change these regions have undergone. 

 That this has really taken place as here indicated, we think is 

 proved by the following considerations. Not more than twenty 

 (probably a smaller number) out of about one hundred land birds 

 of Celebes at present known are found in Java or Borneo, and 

 only one or two of twelve or fifteen Mammalia. Of the Mam- 

 malia and birds of Borneo, however, at least three-fourths, probably 

 five-sixths, inhabit also Java, Sumatra, or the peninsula of Malacca. 

 Now, looking at the direction of the Macassar Straits running nearly 

 north and south, and remembering we are in the district of the 

 monsoons, a steady south-east and north-west wind blowing alter- 

 nately for about six months each, we shall at once see that Celebes 

 is more favourably situated than any other island to receive stray 

 passengers from Borneo, whether drifted across the sea or wafted 

 through the air. The distance too is less than between any of the 

 other large islands ; there are no violent currents to neutralize 

 the action of the vrinds ; and numerous islets in mid-channel offer 

 stations which might rescue many of the wanderers, and admit, 

 after repose, of fresh migrations. Between Java and Borneo the 

 Avidth of sea is much greater, the intermediate islands are fewer, 

 and the direction of the monsoons ahnff and not ao'oss the Java 

 sea, accompanied by alternating ciu'rents in the same direction, 

 must render accidental communication between the two islands 

 exceedingly difficult; so that where the facilities for intercom- 

 munication are greatest, the number of species common to the two 



