360 SMITH. 



the youngest. The principal tectonic lines nin generally north and 

 south, thus conforming approximately to the Asiatic coast line. One 

 of the deepest parts of the Pacific lies directly off the east coast of this 

 island,^ and hence Mindanao marks the eastern edge of the continental 

 horst. 



So far as we now know, there are no rocks in Mindanao and Sulu 

 which we can with certainty say are older than the Tertiary. There are 

 two good reasons for this : First, this territory apparently has emerged 

 from the sea so recently that the streams have not been able to cut 

 through the overlying formations to the older ones below; and second, 

 but little has been done in the way of excavation and boring. Mindanao 

 differs in this respect but slightly from the rest of the Archipelago. 



As it is almost impossible anywhere to see other than very limited 

 geologic sections, we must leave much to conjecture in regard to the 

 succession of formations in Mindanao. Still less can be observed in 

 Sulu, where practically everything is blanketed by recent volcanics. 

 However, by piecing the isolated facts together we can arrive at the 

 following provisional scheme : 



Provisional stratigrapkic scheme. 



Recent : Miocene : 



Coral reefs. Limestones and shales. 



Piedmont deposits. Coal ( ? ) 



Eiver alluvium, etc. Oligocene and Eocene: 



Raised beaches. Coal measures. 



Andesites. Unconformity ( ?) 



Basalts, etc. Uncertain but probably Tertiary: 



Pliocene: Schists. 



Limestones. Unconformity. 



Volcanics. Deep-seated igneous with eonglo- 



Unconformity. merates and various intrusive 



rocks. 



II. DISTEICTS. 

 Zamboanga. 



Physiography. — In the Zamboanga district I shall include the large 

 Island of Basilan which is off the southern end of the peninsula, and 

 the long narrow peninsula itself up to a line extending from Sindangan 

 Bay south to Sibuguey Bay. This territory is characterized by its rugged 

 topography, indented coast line, lack of any considerable coastal plain, 

 numerous reefs, short, shallow and swift rivers, heavy forests, and few 

 settlements of any importance. 



The only large settlement is Zamboanga, situated at the edge of the 

 broad plain at the southern extremity of the peninsula. As I have 



'Ann. d. Hydrog. u. inar. Met. (1906), 556. 



