XI, A, 5 



Pratt: Philippine Lakes 



225 



that an eruption of Taal Volcano was responsible for the separa- 

 tion of the lake from the sea, while Becker ® explained its isola- 

 tion from the rest of the Central Plain of Luzon as the result of a 

 slight undulation in surface. Adams ^ argues with considerable 

 reason that the position of the lake marks a fault line which 

 extends in a general north-south direction and that the escarp- 



FlG. 1. Laguna de Bay, southwestern Luzon. (Depths and elevations are given in meters.) 



ment of tuff to the west of the lake represents one face of a 

 raised fault block which has retreated to the west through erosion. 

 The elevation of the block on the opposite side of this fault 

 separated the lake from Manila Bay, but was gradual enough 

 to permit the erosion of the outlet through Pasig River. 



It is said that the former town of Bay on the southern shore 



' Geology of the Philippine Islands, 21st Annual Rep. U. S. Geol. Surv. 

 (1901), reprint, 77. 

 ' Op. cit., 97. 



