246 APPENDIX. 



extend parallel to the shore, and they are not unfrequently 

 connected in their middle parts by short transverse banks 

 with the mainland. The sea is generally profoundly deep 

 quite close to them, as it is near most parts of the coast 

 of the mainland; but this is not universally the case, for 

 between lat. 15 and 17 the water deepens quite gradually 

 from the banks, both on the eastern and western shores, 

 towards the middle of the sea. Islands in many parts arise 

 from these banks; they are low, flat-topped, and consist of 

 the same horizontally stratified formation with that forming 

 the plain-like margin of the mainland. Some of the smaller 

 and lower islands consist of mere sand. Capt. Moresby 

 informs me, that small masses of rock, the remnants of 

 islands, are left on many banks where there is now no dry 

 land. Ehrenberg also asserts that most of the islets, even 

 the lowest, have a flat abraded basis, composed of the same 

 tertiary formation: he believes that as soon as the surf 

 wears down the protuberant parts of a bank, just beneath 

 the level of the sea, the surface becomes protected from 

 further abrasion by the growth of coral, and he thus 

 accounts for the existence of so many banks standing on a 

 level with the surface of this sea. It appears that most of 

 the islands are certainly decreasing in size. 



The form of the banks and islands is most singular in 

 the part just referred to, namely, from lat. 15 to 17 , where 

 the sea deepens quite gradually: the Dhalac group, on the 

 western coast, is surrounded by an intricate archipelago of 

 islets and shoals; the main island is very irregularly shaped, 

 and it includes a bay seven miles long, by four across, in 

 which no bottom was found with 252 feet: there is only one 

 entrance into this bay, half a mile wide, and with an island 

 in front of it The submerged banks on the eastern coast, 

 within the same latitudes, round Farsan Isld., are, likewise 



