IV.] SULU ZOOGBAPHICALLY PHILIPPINE. 79 



The same evidences of absence of a former connection with, or 

 at least t)f a long separation from, Borneo are apparent if we turn 

 to the mammals. The pig is, in all probability, an introduced 

 species. A monkey is said to be found on Sulu w^hich is probably 

 Macaciis cynomolgus, but we did not shoot it, and the only species of 

 deer existent on the island we were unfortunate enough to fail in 

 obtaining. No other animals, except the rat and various Pteropi, 

 came under our notice during the whole of our visit. In Borneo 

 the naturalist might obtain twice as many species in a single day. 

 Mr. Burbidge's researches in the botany of the archipelago tell the 

 same tale. " In Sulu," he says, " the flora showed a marked 

 resemblance to that of the Philippine and Celebes groups." ^ 



Zoographically, then, Sulu is purely Philippine, just as it is 

 politically by the treaty of 1885. If we consult the charts of the 

 islands we shall see the explanation of it. The Strait of Basilan 

 shows soundings of from thirty to forty fathoms only, and from that 

 island south-westwards to Tawi-tawi the depths are such that a ship 

 could easily anchor at almost any point on the submarine bank 

 connecting the group. West of Tawi-tawi, however, the level of 

 the sea-bottom completely changes, depths of 100 fathoms or more 

 being obtained close in-shore, while in the fairway of the Strait, 

 which is known as the Sibutu Passage, Captain Chimnio was 

 unable to get bottom at 500 fathoms. The distance across the 

 Strait is about eighteen miles, and the surveys hitherto made seem 

 to show an equally precipitous slope of the eastern shores of Sibutu 

 Island. There is at present no exact information with regard to 

 the soundings between Sibutu and Borneo, one point of which, 

 Tanjong Labian, is distant only twenty miles, but since many 

 islets, reefs, and sand -cays are known to intervene, it is almost 

 certain that they are not of any great depth. The Sibutu Passage 

 thus seems to be the natural delimitation of the Philippine Archi- 

 pelago, and the traveller crossing it eastwards from Borneo 

 experiences a change in the nature of his surroundings, which, 

 1 "The Gardens of the Sun," by F. AV. Burbidge, p. 343. 



