GEOLOGIC RECONNAISSANCE OP SOUTHWESTERN LUZON. 97 



deposited during a long period of time. The formation varies from fine- 

 grained., water-laid strata to coarse, brecciated deposits, agglomerates and 

 conglomeratic phases. The examination of samples obtained from drill- 

 ing deep wells shows interstratified marine sands and some clayey beds. 



It is very difficult to distinguish between the water-laid tuff and the 

 subaerial deposits because of the similarity in the materials and the 

 absence of exposures at critical points. On the divide between Bay Lake 

 and Manila Bay in a railwa} r cut some shark's teeth were found in a 

 stratum containing waterworn pebbles. The bed is evidently a marine 

 or estuarine deposit. The elevation of this point is about 40 meters 

 above the sea'. The presence of the fish teeth indicates an emergence 

 which may be correlated with the change of level indicated by the marine 

 conglomerates on the flanks of the western cordillera. Smith collected 

 some fragments of a mammalian tooth near the Loboo Mountains at a 

 considerable elevation, which, however, was not determined by measure- 

 ment. He believed the tooth to belong to the Bovidae. An examination 

 of the pieces which have been preserved showed that they correspond 

 fairly well with the teeth of the Ccrvidae and do not differ much from 

 those of the living Philippine deer. This tooth may have been buried 

 in late subaerial deposited tuff and the presence of plant impressions, 

 especially of blades of grass or rice in the same beds, is corroboratory 

 evidence. The mammalian tooth found in the Pasig well at a depth of 

 between 80 meters and 85 meters, appears to belong to an extinct species. 

 The formation ma) r , however, be marine and it may have been buried in 

 deep water deposits. The locality where the fish teeth were found and 

 the situation of the Pasig well are not very widely separated. Outcrops 

 of the tuff at intermediate localities appear to be water laid and contain 

 many plant remains. 



The higher portion of the tuff area is a ridge between Mount Sungay 

 and Mount Batulao called cordillera of Tagay-tay on d' Almonte's map. 

 The southern face of this ridge presents rather steep slopes and some 

 escarpment, while the northern side of the ridge slopes gradually toward 

 Manila Bay. It has been argued by some writers that this ridge re- 

 presents a portion of the base of the former lofty cone of Taal Volcano. 

 The elevation of the ridge varies from 500 to 600 meters, which is con- 

 siderably in excess of the highest marine deposits on the flanks of the 

 western cordillera. There are some basalts in the southern face of the 

 ridge, but most of the exposures are beds of stratified tuffs. Certain of 

 the beds appear to be water-laid. If any part of the higher beds in this 

 ridge were deposited in the sea, it indicates a greater elevation of the 

 locality than has taken place in the adjacent areas. It is not improbable 

 that the ridge, together with two mountains which form its determina- 

 tions, is the southern portion of a fault block which has been lifted. 



