GEOLOGIC RECONNAISSANCE OF SOUTHWESTERN LUZON. 89 



rounding it there is a creseentic ridge which probably represents a part 

 of the older outer crater (fig. 7). The region around the base of Ma- 

 quiling has not been thoroughly studied, but some of the hills to the 

 west appear to have been formed by subsidiary vents and one to the 

 west of the road between Calamba and Santo Tomas, which was ex- 

 amined, gave evidence of being a cinder cone, but without any indica- 

 tions of a crater. 



Eruptives. — Under this bead will be discussed the mountains of the 

 southeastern volcanic district which do not retain evidences of distinct 

 craters or are not so close to the extinct volcanoes as to appear genet- 

 ically related to them. 



To the south, on the structural line which includes Talim Island and 

 Maquiling, stands the elongate Malarayat-Sosoncambing Mountain. To 

 the east of Maquiling and to the northwest of Banahao there is a group 

 of low mountains to which here is given the name Calauang Mountains. 

 Further east in the tuffs near Cavinti and to the northward there are 

 some outcrops of igneous rocks which are not shown on the geologic 

 map. A small hill occurs at Pagsanjan and to the east of Pagsanjan 



Pig. 7. — Sketch Showing the Extinct Cinder Cone Ceero de la Mesa and 

 Outer Crater Rim as Seen Looking South from Calamba Railway Station. 



the country contains some topographic features which indicate eruptives. 

 Southeast of the Pico de Loro Mountains there is a group of peaks 

 which are surrounded by the tuff formation. To the south of Nasugbu 

 some exposures of igneoiis rocks were found which belong to the sub- 

 structure of the Santiago Peninsula. In the peninsula south of Lemery 

 there is another group of eruptives. 



Finally, there should be mentioned Mount Sungay to the north of 

 Taal Lake, Mount Butulao to the west of the latter, but a considerable 

 distance from it, and Mount Macalod standing on the southeast margin 

 of the lake and having a high precipice facing it. The relation of these 

 eruptive masses, with the exception of Malarayat-Sosoncambing which 

 is considered to be on the north-south structural line that includes 

 Maquiling and Talim, is far from clear. It appears that the eruptives 

 lying in the peninsular area have been added to the mainland of Luzon 

 Island by the gradual extension of the tuff formations. The Calauang 

 group of lower peaks is very irregular. The igneous rocks further to 

 the east near Cavinti and Pagsanjan are nearly covered by the tuff 



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