212 The Philippine Journal of Science 1914 



along the eastern edge of the Central Plain. Artesian wells 

 in the vicinity of Angat near the edge of the plain have gone 

 down to a depth of 150 meters without passing through these 

 beds. At Moronco, west of Angat, the uppermost member is 

 coarsely fragmental tuff, but at Angat the f ragmen tal tuff has 

 been removed and beds of fine tuff and clays are exposed at the 

 top of the series. The artesian well records show thick beds of 

 coarse gravel in clay, together with fine tuffs, clays, and sub- 

 ordinate fine clean gravel. The fine tuff and clay exposed by 

 Angat River carry numerous pieces of carbonized wood and also 

 numerous calcareous concretions. The strata lie nearly hor- 

 izontal, but minor displacements through faulting are to be 

 observed. Fossil leaves of species closely related to those at 

 present living are found in the clays, and the formation is 

 believed to be not older than Pleistocene. 



Miocene formations. — The greater part of the area mapped 

 is occupied by sedimentary rocks of late Miocene age. This 

 formation extends across the area from north to south in a 

 belt of varying width. The thickness in the exposed sections 

 also appears to vary, as may be seen from an inspection of the 

 graphic sections (fig. 3). It has not been possible to make 

 close measurements of the thickness of the series because of the 

 absence of continuous exposures, but it is believed that the 

 maximum thickness is close to 2,000 meters. The beds are 

 inclined at many places steeply toward the west, the strike 

 varying from north 30° west south of the ore deposits to north 

 30° east in the northern part of the area. There are numerous 

 local overturns or folds, but the formation as a whole is tilted 

 away from the cordillera. There appears to have been dis- 

 placement at a number of places along faults about parallel 

 with the strike, but the study has not been sufficiently detailed 

 to supply definite information with regard to faulting. 



A thin discontinuous limestone made up of well-preserved co- 

 rals marks the top of the series, and immediately below it is a 

 sandy, brownish yellow shale. It seems probable from the 

 results of studies of similar formations elsewhere in the Philip- 

 pines that these two members are as young as the Pliocene. 

 Underlying the shale is a much more prominent limestone which 

 can be traced south in almost continuous exposures to the Binan- 

 gonan limestone in Rizal Province. The age of the Binangonan 

 limestone has been definitely fixed by Smith ^ as Miocene, to which 



"This Journal, Sec. A. (1913), 8, 242. 



