RECONNAISSANCE OF MINDANAO AND SULU : III. 363 



Analysis of Basilan gahhro. ' 





Per cent. 





Per cent. 



SiOo 



52.47 

 17. IG 

 1.89 

 8.08 

 5.32 

 9.21 

 0.82 

 0.36 

 1.59 



H-jO loss on ignition 



0.80 

 1..53 



Trace. 



Trace. 



Trace. 

 0.36 



AI0O3- 



TiOo • J- 



FeoOa -- 



P.,05 -_ 



FeO 



MgO 



CI _. 



S 1 



MnO .- 



CaO 



Na.,0 ■- 



Total .. 



99.59 



K»0 





H.>0 below 105°... 





Turning attention next to the vicinity of Zamboanga, we find a 

 coastal plain perfectly flat and with a width varying from one to ten 

 kilometers. The substructure is a coral reef or a series of them. Coral 

 is growing in the sea at the edge of this plain at the present time, and 

 in walking from Zamboanga north to the Zamboanga gorge, at least 

 two older reefs which marked the former edges of the plain, are crossed. 

 A varying thickness of detritus washed from the mountains is super- 

 imposed upon this substructure, but no consolidated formations are 

 encountered. A broad platform extends out from the gorge, really a 

 very gently sloping alluvial fan, which is known locally as the mesa. 

 There is a depressed area just in front of and parallel to the gorge which 

 marks a former position of the coast line. This is termed a cuesta. 

 At the gorge we found a vast cliff of andesite. Near the barrio of 

 ■ Masiay we again encountered this volcanic rock outcropping on the 

 banks of the San Eoque Eiver; here it does not occur as a cliff, but 

 in low hills. This rock has all the characteristics of a surface flow, 

 but it is a very old one, as the vesicles or 'Tjlow holes" have been filled 

 with secondary mineral matter. At the foot of the hill on which is 

 located "Station M" on Captain Moore's map, I found a calcareous 

 formation with true bedding planes dipping at an angle of 29° to the 

 southeast and with a strike north 42° east. This is the only outcrop of 

 a sedimentary I have found near Zamboanga. 



A well was sunk to an approximate depth of 165 meters on the military post 

 at Zamboanga, with the hope of finding water, but without result. It is barely 

 possible that a supply of water might have been obtained by going deeper, but it 

 seems to me that on account of the loose material composing the Zamboanga 

 plain and the probable impounding of any water which has come from the lava 

 formation by the old reefs which occiir between the gorge and Zamboanga, it is 

 not likely that the project would have been successful within a reasonable ex- 

 penditure of money. If the sediments, which I noted near the "Station M", 

 persist in their dip, they would never emerge again at the edge of the plain. 



'Analysis by E.. R. Williams, Bureau of Science. 



