from the Sulu Archipelayo. 241 



depth^ the charts showing 590 fathoms ' without bottom/ 

 so that this deep Sibutu Passage seemed to form the natural 

 line of delimitation between the Borneau and the Philip- 

 pine groups of islands and between their respective faunas. 

 Capt. Field, of H.M.S. ' Egeria/ has been recently sur- 

 veying this part of the coast of Borneo, and I suggested 

 to him that it would be a point of some scientific interest 

 to ascertain the real depth of the Sibutu Passage. This 

 he very kindly did, with the result that the deepest sound- 

 ing obtained was 267 fathoms, while one cast showed as 

 little as 139 fathoms. Capt. Field informed me that he had 

 sounded as nearly as possible on the spot where the chart 

 records ' 500 fathoms — no bottom ' without finding any such 

 depth, and that he thought that the former record might have 

 been due to errors arising from the less perfect sounding- 

 apparatus in use in former days. But not only is the Sibutu 

 Passage much shallower than Guillemard was led to suppose 

 it to be, but Capt. Field^s survey on the western side of the 

 island shows that it is connected with the 100-fathom frinffiner 



•o o 



bank of Borneo by a very narrow isthmus^ on which the 

 shallowest sounding seems to be one of 75 fathoms, — so that 

 it can only just be said to be geographically a part of Borneo 

 as defined by the 100-fathom line of soundings. I may 

 mention that Sibutu is mainly composed of recent coral 

 limestone, raised not many feet above the sea; but there is a 

 hill of volcanic rock and a crater-lake, which I did not myself 

 see. The Tawi-Tawi Islands appear to be all either volcanic 

 or recent limestone. 



"The Black-headed Pitta in Sibutu appeared to me to be 

 nearer to Pitta muelleri than to P. sordida, which is the Tawi- 

 Tawi species, but I have no skins to compare it with. Beside 

 the birds of which I send skins. Halcyon chloris was exceed- 

 ingly abundant both on Sibutu and on the other islands; 

 and at Bongao Cuncuma /euco(/aster, a. species of Mlcrohieraa?, 

 Turtur dussumieri, Carpopliaga bicolor, and Gallus bankiva 

 were observed, together with a species of Lalage and a bird 

 which I think was Dendrobiastes basilanica, but I could not 

 be sm'e. I saw also Carpophag a dickering i on Sibutu/'' 



