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Show 1889.] RELATIONSHIPS OF PALAWAN ISLAND. 227 inquiry into the physical geography of the group and the relationship of the mammalian fauna ; and they appear to me to be, when taken together, of sufficient weight to justify the inclusion of these islands definitely as an integral portion of the Bornean group in the western sub-area of Indo-Malaya, and this notwithstanding the probability that future research may show that in some classes of animals the Philippine element preponderates, and that many of the small low islets immediately confronting the Philippines on the eastern margin of the Bornean bank, such as the Cuyos, no longer retain any trace of their original western element. If the origin of the Palawan fauna here suggested be the true one, then the highlands which are still wholly unexplored, and which attain to an elevation of between 6000 and 7000 feet, will probably be found to exhibit a yet more marked predominance of Bornean forms than is presented by the low country. The islands of Cagayan-Sulu and Sibutu, which have been treated, like Palawan, as belonging to the Philippines, should be regarded similarly as natural component portions of the Bornean group. They are both situated on the edge of the fringing submarine bank of north-eastern Borneo. The first named has been visited by Dr. Guillemard, who obtained a small collection of the birds, comprising 15 species, and who pointed out1 that, judging from the position of the island and the character of its avifauna, it should be regarded as related to the Bornean instead of, as heretofore, to the Philippine group. The only peculiar species obtained was Mixornis cayayanensis, a representative form of M. borneensis. The Island of Sibutu has never been visited by a naturalist, and although of small extent it is of interest in view of its close proximity to the southern extremity of the Philippine Archipelago. Dr. Guillemard, again, was the first to show2 that this island should probably be considered as an outlying portion of Borneo; and as his remarks contain all the information about it, I cannot do better than quote them, premising that the Tawi-Tawi Islands, of which, in political geography, Sibutu is one, form the south-western extension of the Sulu Archipelago, which is admittedly Philippine in the character of its fauna. Dr. Guillemard says : - " West of Tawi-Tawi 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 (the Sibutu Passage) Captain Chimmo was unable to get bottom at 500 fathoms. The distance across the Strait is about 18 miles, and the surveys hitherto made seem to show an equally precipitous slope of the eastern banks of Sibutu Island. W e are at present without exact information as to the soundings between Sibutu and Borneo, one point of which, Tanjong Labian, is distant only 20 miles ; but as many islets, reefs, and sand-cays are known to intervene, it is almost certain that they are not of any great depth. This Sibutu Passage thus seems to be the natural delimitation of the Philippine Archipelago, and though of the only two species (of birds) obtained, or said to have been obtained, from 1 P. Z. S. 1885, p. 418. 2 P. Z. S. 1885, p. 250. |
