102 ADAMS. 



and the subsidence and collapse of the man}' cones which have been 

 formed within its area during prehistoric eruptions. The process of 

 formation has been continued to a small degree during historic time. 



The fact that the caldera is occupied by a lake prevents in a large 

 measure the study of its origin. However, in the brief notes concerning 

 the two eruptions of Taal, it is recorded that within Taal Lake a new 

 cone arose as an island and subsided, leaving as its remnants two small 

 islands which lie to the east of Taal Volcano. In another eruption, a 

 portion of the shore of Taal Lake near the former site of the settlement 

 of Taal subsided below the water. Many who see the sheer face on the 

 west side of Mount Macalod form the opinion that a large mass of the 

 mountain has subsided into Taal Lake, and as substantiating this idea 

 it is pointed out that the deepest part of the lake is ■ found near this 

 mountain. While studying the shores of the lake it was observed that 

 in certain parts they are precipitous, while in others they are eroded 

 into gentle slopes. It may be that some of the precipitous shore lines 

 are due to recent faulting and displacement, but it will require a detailed 

 study to prove this. Anderson, 4 in his article on Aso Volcano in Japan, 

 has given a list of 31 important calderas, among which he mentions 

 Taal. He points out three ways in which calderas may have originated, 

 namely, by being built up around a vent of great magnitude, by the 

 explosive removal of a volcanic mountain or by the subsidence of the 

 area inclosed within its walls. The writer does not feel competent to 

 discuss the theory that Taal Lake has been formed by explosions as has 

 been suggested by Becker, but not fully outlined by him in its applica- 

 tion to the volcanic center of Taal. 



There are many objections to Centeno's elaboration of Zuniga's theory 

 that Taal once had a high volcanic cone. Centeno assumed that the 

 ridge ( Cordillera of Tagay-tay, elevation 500 to 600 meters) between 

 Mount Gonzales and Batulao represents a portion of the base of a 

 former cone which he reconstructed, theoretically assigning to it an 

 elevation of 3,750 meters. The ridge, however, does not have the form 

 of a portion of the base of a cone and moreover there does not remain 

 any evidence of similar features to the east and south of Taal Lake, but 

 instead, the tuff formation is nearly horizontally bedded and forms a 

 plain with an elevation ranging from 150 to 250 meters near the lake. 

 A large part of it is certainly water-laid. It is manifestly incorrect to 

 assume that Mount Macalod is a part of the southern base of a former 

 cone of Taal as Centeno has argued, since it is an eruptive mass unlike 

 the Tagay-tay ridge. It is suggested that the ridge to the north of 

 Taal Lake may be due to elevation of a fault block. While there is 

 little certainty that this is true, it would be consistent with the general 



4 The Japanese Volcano Aso and Its Large Caldera. Journ. Geol. (1908), 

 16, No. 6, Univ. Chicago Press. 



