178 
MR. A. R, WALLACE ON THE ZOOLOGICAL 
now surrounding it, and obtained some part of its fauna before 
they came into existence. They point to the time when a great 
continent occupied a portion at least of what is now the Indian 
Ocean, of which the islands of Mauritius, Bourbon, <fcc. 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 Guinea 
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 occurred subsequent to the submergence of 
both these great southern continents ; and the breaking up and 
separation of the islands of Sumatra, Java, and Borneo 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 winds ; 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 
width of sea is much greater, the intermediate islands are fewer, 
and the direction of the monsoons along and not across the Java 
sea, accompanied by alternating currents 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 
