PHYSIOGRAPHY OF THE PHILIPPINE ISLANDS. 5 



paratively small area occupied by Mounts Aroroy, Bagadilla, and Ka- 

 lakbao. The summits of these hills lie in an almost direct north and 

 south line^ although the individual hills show a marked northwesterly 

 trend. This trend is in a large measure due to the greater resistance to 

 erosion offered by the quartz veins, which 23i'actically all show a north- 

 westerly strike. 



Mount Aroroy (elevation, 250 meters) shows this trend very clearly, 

 in a long, cogon-covered point running out from the summit to the 

 northwest. A large vein has been opened on the summit of the mountain 

 and its continuation along the ridges is shown by bowlders of iron- 

 stained cpiartz. Mount Bagadilla (elevation, 340 meters) shows two 

 large ridges running off to the northwest, the southern certainly being 

 due to the presence of quartz veins and the northern probably to the 

 same cause. The veins of the southern ridge of Mount Bagadilla 

 continue across the Guinobatan Eiver and there form the l)ackbone 

 of Mount Kalakbao (elevation, 200 meters). Mount Kalakbao is a 

 long ridge following the northwest strike of the veins. It contains at 

 least ten veins,' including the best known in the district. Only two 

 veins have been found across Kaal Brook to the soutlieast, and apparently 

 none continue farther southeast into Mount Vil-lon. It seems as if the 

 northerly stretch of the Guinobatan Eiver on the west and Mount Vil-lon 

 on the east form the boundaries of the Aroro}' vein system, a line 

 southeast from the turn of the Guinobatan Eiver at the Gold Bug prop- 

 erty, and between Mount Kalakbao and Panique Hill l)0unding the 

 system on the south. 



The drainage features of the Aroroy district also show marked pe- 

 culiarities. In the extreme north of the district the Buyuan Eiver has 

 a northerly course near its mouth, although farther up the stream the 

 course is northwesterly. The two small streams near Aroroy, Ambulong 

 and Lubigang Creeks flow northwesterly into the mangrove swamp 

 which surrounds Aroroy, between narrow, northwesterly ridges. An 

 unexj)lained feature of the course of Lubigang Creek is the sharp bend 

 it makes into Mount Aroroy. There seems to be nothing in the structure 

 of the rocks to account for this, nor does it seem probable that a north- 

 westerly area of weakness would be developed for such a short distance. 



Bangong Creek flows between Mount Aroroy and Mount Bagadilla, 

 but cuts obliquely across the strike of the veins instead of running 

 parallel, as would be the case with perfectly adjusted drainage. An- 

 other peculiarity of this stream is in its headwaters. It rises east of 

 Mount Aroroy and flows at first to the southeast, draining country which 

 would naturally be expected to be a part of the drainage basin of one 

 of the creeks flowing toward Aroroy, or of the Buyuan Eiver. It is 

 evidently a capture of the headwaters of Balagting Creek, a stream 

 flowing southwest, tributary to the Guinobatan Eiver. 



