MINDANAO AND SULU : II. PHYSIOGRAPHY. 



361 



On the Island of Jolo tapioca and coconuts are the chief products. 



Basilan has several rubber plantations. 

 Siasi and Lapac, just across a narrow 

 strait from it, are now being given 

 over to sago, coconuts, and tapioca. 



The striking feature about this little 

 archipelago is of course the multitude 

 of inlets with innumerable little bays 

 and proportionally great length of 

 coast line. These features make this 

 one of the best possible resorts "for 

 pirates and hardly a year passes but 

 the United States troops have some 

 slight encounters with them. How- 

 ever, piracy has now practically ceased. 



There are three physiographic phe- 

 nomena which I desire to call attention 

 to before leaving this subject. They 

 are: 1. Atolls; 2. Monadnocks; 3. 

 Crater lakes. 



Atolls. — I shall not repeat here a 

 description of an atoll. It is sufficient 

 to say that there are several more or 

 less perfect ones in this region, some 

 with lagoons of considerable size in the 

 center, others with only shallow de- 

 pressions, probably a result of eleva- 

 tion and filling of the former basins. 



Monadnocks. — I have used this 

 word for want of a more concise term 

 to describe .the phenomena seen on 

 some of the islands, particularly Ma- 

 rongas, a very small island just north 

 of the town of Jolo. A photograph 

 of these peculiar humps sticking out 

 of the sea is shown on Plate V. They 

 are simply due to hard, resistant basalt 

 dikes which have intruded the sedi- 

 ments and have withstood sea action. 



Crater lakes. — There are several of 

 these on the Island of Jolo. (Plate 

 VI.) Silt Lake near the constricted 

 portion of the island is particularly 

 noteworthy. However, by far the 

 most striking of these lakes occur on 



