310 SMITH. 



The southern portion of the central plain of Luzon is modified by tuff 

 deposits which in places are found in fairly thick beds. The log of a well 

 *put down near Manila, which is situated at the lower end of this plain, 

 shows the character of this material very well. 



Log of well at Pasay, Rizal Province. 



feet to 18 feet. Soil, sand and sea shells. 



18 feet to 36 feet. Gray silt, pebbles, shells. 



36 feet to 50 feet. Gray silt, with shells. 



50 feet to 63 feet. Yellow silt, pebbles, small calcareous concretions. 



63 feet to 83 feet. Yellowish-gray silt, small calcareous pebbles, shells. 



83 feet to 87 feet. Fine to coarse basaltic pebbles and tuff. 



87 feet to 113 feet. Yellow-gray sand, some clay, fragments of soft tuff 

 113 feet to 135 feet. Yellow-gray tuft'. 

 135 feet to 160 feet. Yellow-gray tuff, clayey. 



160 feet to 180 feet. Yellow sand and tuff, small basaltic pebbles. 

 180 feet to 199 feet. Light yellow, gray tuff. 

 199 feet to 228 feet. Light gray tuff. 

 228 feet to 248 feet. Tuff with fine basaltic pebbles. 

 248 feet to 276 feet. Light yellowish gray tuff. 

 276 feet to 290 jeet. Yellow tuff, small basaltic pebbles. 

 290 feet to 318 feet. Tuff and small basaltic pebbles. 



318 feet to 332 feet. Tuff and pebbles from basaltic rock. , 



332 feet to 350 feet. Yellowish-gray tuff. 

 350 feet to 370 feet. Basaltic pebbles and sand with tuff. 

 370 feet to 393 feet. Tuff, small basaltic pebbles. 

 393 feet to 422 feet. Tuff. 

 422 feet to 432 feet. Tuff, fine grained. 

 432 feet to 463 feet. Tuff, fine grained. 



463 feet to 483 feet. Fine, dark sand, some clear grains, fragments of tuff, basal- 

 tic pebbles. 

 483 feet to 506 feet. Slightly clayey tuff, basaltic pebbles. 

 506 feet to 530 feet. Fine-grained tuff, light gray. 

 530 feet to 546 feet. Fine-grained tuff, light gray. 

 546 feet to 570 feet. Dark sand, some clear grains. 

 570 feet to 594 feet. Tuff, with small basaltic pebbles. 

 594 feet to 620 feet. Clay and basaltic pebbles. 

 620 feet to 634 feet. Yellow clay with small basaltic pebbles. 

 634 feet to 660 feet. Dark sand, fairly fine. 

 660 feet to 690 feet. Dark sand with few basaltic pebbles. 

 690 feet to 713 feet. Fine gray tuff. 

 713 feet to 743 feet. Basaltic pebbles and fragments of tuff. 



There is an additional feature of this plain not found in the majority 

 of the others, namely, there has been a subsequent warping so that two 

 streams, the Agno and the Bued, coming out of the mountains from the 

 north, are turned westward and finally flow northwest into the sea at 

 Lingayen Gulf, while south of this uplift the streams flow south to Manila 

 Bay. ' 



