GEOLOGIC RECONNAISSANCE OF SOUTHWESTERN LUZON. 75 



this area into low-lying land and it has been gradually aggraded and 

 extended by the sediments brought by the river system. 



The southern end of the Candaba swamp which has a larger extent 

 beyond the limits of the geologic map, lies on the eastern border of the 

 alluvial area, between Baliuag and Apalit. A part of this swamp is 

 included within the alluvial area of the geologic map. During the 

 rainy season it is partially overflowed, but during the dry months a 

 large j:>ortion of it is cultivated. There has been some talk of attempting 

 to reclaim it to cultivation by means of drainage canals. 



Various opinions are current in regard to the origin of this swamp; 

 one is that it represents a remnant of the retreating sea which has been 

 freshened, and, in support of this view, it is stated that it contains a 

 brackish water fauna. However, since it receives a large amount of 

 fresh water during the rainy season, and has outlets, there is little reason 

 to believe that it contains any salts which remain as a result of the 

 impounding of an arm of the sea. A second theory in regard to this 

 swamp is that it represents an area of subsidence. This is not very 

 fully discussed in any writings, but is somewhat substantiated by Centeno's 

 report on the earthquake of 1880, in which he records that a great many 

 cracks opened in Nueva ficija Province along a zone which, if continued 

 southward, would pass near the Candaba swamp. A simple explanation 

 is that the Candaba swamp represents an area which lying between the 

 main channel of the Pampanga Kiver and the Quiangan Eiver, has failed 

 to receive sufficient sediments to build it up as rapidly as the remaining 

 portion of the delta. 



EASTERN CORDILLERA. 



Some of the earlier descriptions of the formations of this region are 

 faulty, and certain of the conclusions reached are based upon reports 

 that have since proved untrustworthy and conjectures which were sup- 

 ported by no reliable information. This is especially true in regard to 

 the so-called older crystallines and slates and the possibility of the 

 presence of the Carboniferous. 



Schists. — On Von Drasche's map two areas of older crystallines are 

 shown in the eastern cordillera. The color representing them bears the 

 sub-legend "Gneiss, Chlorite-hornblende schist, etc." The northern area, 

 lying to the east of Angat, was not visited by Von Drasche, and it is 

 probable, as Becker has suggested, that this area was mapped on the 

 strength of Itier's statement which is quoted by Von Drasche as follows: 

 "In Angat at the base of the foothills of the cordillera of Luzon, there 

 exists no evidence of volcanic products, and the rocks carried by the 

 river are diorite amygdaloid, spilite amygdaloid, diabase, epidote, dolomite 

 and porphyry . . . ." Eoth says that the iron deposits near Angat 

 indicate the presence of crystalline slates, but his course of reasoning is 

 not clear. It is possible that he was influenced by the fact that iron 

 deposits are found in the Camarines associated with older crystallines. 



