RECONNAISSANCE OF MINDANAO AND SULU : III. 361 



already said, Zamboanga is a "gate city," its importance being due to its 

 location at the intersection of several trade routes. It owes very little 

 to the country immediately back of it. We shall see the importance of 

 this when we compare it with such localities as those of Cotabato and 

 Butuan. Zamboanga does not even lie near a river. The Tumaga, 

 hardly deserving of the name of river, which rises in the mountains, 

 formerly emptied into the sea somewhere near Zamboanga, but now it 

 turns sharply to the east near the barrio of Santa Maria and has its 

 mouth at Port Masinloc. The greater part of the coastal plains of 

 Zamboanga and Basilan are largely inhabited by iloros, a constantly 

 shifting population, living most of the time in boats and coming ashore 

 only to trade. The rugged interior of Basilan is peopled by Yakans, who 

 are called "Hill Moros," and the Zamboanga Peninsula by Subanuns. 

 The Subanuns are a very primitive people who have retreated before the 

 advance of the Moros and who now live in a nomadic state, constantly 

 changing their abodes from one clearing to another. These clearings 

 are known as Jcainffins. 



Stratigraphy. — Good geologic sections are, as elsewhere, very difficult 

 to find in the Zamboanga Peninsula. However, some very satisfactory 

 exposures of limited extent may be seen in the gorge of the Tumaga 

 Eiver and at several points along this stream to the north. By piecing 

 together the information gathered from scattered outcrops, we can ap- 

 proximate the stratigraphic succession. The basal rock, as in the northern 

 islands, is probably a diorite, although I have seen this only in pebbles 

 in the streams. Presumably above this diorite lies a basal conglomerate. 

 The next formation in the peninsula proper is a schist, which may simply 

 be metamorphosed sandstones and shales. This schist is found best 

 exposed in the beds of the streams which run along the long axis of the 

 peninsula. It is completely buried in other localities by later volcanic 

 flows and alluvium, but can be seen well for about twenty-four kilo- 

 meters along the bed of the Tumaga Eiver. This schist dips to the east 

 at an angle of about 4-5° and with a strike of nearly 40° east. It is a 

 grayish to green rock, with a considerable development of chlorite along 

 the plains of schistosity, and is characterized by nimierous small stringers 

 of auriferous quartz. In a thin section it is seen to consist of long, 

 frayed-out, green hornblendes with granular quartz and feldspar, with 

 the quartz dominant, these two minerals lying between the fragments of 

 hornblende. The schistosity is very marked in the microscopic slide. 

 The large amount of quartz seems to confirm the supposition that it is 

 a metamorphosed sandstone. Other samples show an abundance of chlo- 

 rite and some small sections of apatite. I found an outcrop of fossiU- 

 ferous shale near the gorge of the Tumaga Eiver, the relation of which 

 to the schist I was unable to determine. However, I think it must be 

 much vounger. This shale is identical with that overlving the coal seams 



