362 SMITH. 



Cagayan Sulu, where on the southern side there are three almost circular 

 in form. These are so near the seashore that the sea has broken through 

 the rim of one. 



This closes my brief discussion of the physiographic units in the 

 Island of Mindanao. It can be seen, then, that this is one of the newest 

 and most interesting portions of the whole Philippine Archipelago, a 

 region of slow but continued change. Possibly in time there will be an 

 unbroken land bridge between Borneo and Mindanao. At the conclusion 

 of the next paper, when I shall have discussed the geology, I shall take up 

 the broad questions of human response to natural conditions and attempt 

 to point out some lines along which development is likely to proceed in 

 this great island. 



