GEOLOGIC RECONNAISSANCE OF SOUTHWESTERN LUZON. 103 



structure of the region and would account for the topographic features 

 north of Taal including the escarpment west of Bay Lake. As has been 

 quite fully accepted by all writers, the sea once flowed through a strait 

 between the eastern and western Cordilleras and at that time it oc- 

 cupied a large part of the southwest district. There is no need to as- 

 sume that Taal Volcano has ever formed a peak of great altitude in 

 order to account for all phenomena connected with it, and the topography 

 and structure of the region can be adequately explained if it is considered 

 as a volcano which has always had its crater at a relatively low elevation. 



The outlet of Taal Lake is the Pansipit Biver. This stream has 

 shallow places in which large bowlders of basaltic rock are exposed and 

 some of these seem to be in place. The Pansipit Valley appears to have 

 been eroded by the stream which occupies it. At the outlet of the lake 

 it is bordered by a V-shaped area of low land. Farther on, the river 

 occupies a somewhat tortuous channel bordered by narrow alluvial lands 

 and then flows along the eastern border of a broad delta area. The 

 cutting of the Pansipit Valley has probably been concomitant with the 

 elevation of the land. Some writers have expressed the belief that Taal 

 Lake was once an arm of the sea and that it contains brackish water and 

 a fauna and flora which is in part of marine origin. The water is 

 slightly brackish when tasted but there is no evidence that -it has been 

 salty during recent times because of an admixture of sea water. Its 

 character has probably been temporarily changed during eruptions of 

 Taal. 



Origin of Bay Lake. — There has been a tendency on the part of some 

 writers to consider Bay Lake as having originated through the subsidence 

 of a volcano, or to have been formed as a crater. Dana discovered no 

 evidence that the lake corresponds to a single crater, but he considered 

 Talim Island as a volcanic center, and Bay Island as consisting of the 

 lavas of another vent. As has alreadjr been noted, Hochstetter has 

 suggested that the part of the lake called the rinconada probably marks 

 the position of a subsided crater, but later authors have not concurred 

 with his views. Jagor has described Bay Lake, but he has propounded 

 no well-defined theory of its origin, although one may infer that he 

 considered it to have been at one time an arm of the sea. He found 

 a deposit of marine mollusks (principally Tapes virgineus and Cerithium 

 moniliferum) 3 meters above the level of the lake, near the point of 

 Jalajala Peninsula. He considered these as indicating an elevation of 

 the land. Both states in his notes that these species were determined 

 by Martens and that they belong to the present fauna. 



Von Drasche had no doubt but that the lake was once an arm of the 

 sea similar to Manila Bay at the present time, and that it was separated 

 by an eruption of Taal, and has since become fresh water. Becker calls 

 attention to the fact that Bay Lake is very shallow; the Coast and 



