332 HERRMANN. 



not so, we could adopt the idea that in the same way in which Cebu 

 and Negros form a syncline, which is proved by the coal seams on both 

 islands, the mountains of Zambales and the central ranges form a similar 

 syncline, which in no way is proved and does not agi'ee with the 

 sudden disappearance of the depression to the northward and to the south- 

 ward. 



A profile through Zambales, the central plain, and central Luzon ranges, 

 gives the following view : 



Zambales: mountainous, gabbro serpentine, talcose schists. Central plain: 

 alluvial, volcanic tuffs. 



in the plain: Mount Arayat a basaltic extinct volcano. 



Tlie central ranges : Tertiary limestone and sandstone interrupted by volcanic 

 intrusions. 



In my opinion this tectonic structure can best be explained by a 

 trench break between the Zambales and central mountains. When the 

 ranges were formed during the Tertiary period, the northern Luzon 

 mountains liad their continuation right through the central plain, and 

 reaching over to Mindoro, formed one solid mountain massif from Zam- 

 bales to the east coast. Thereafter on parallel fissures the central part 

 slid down and probably there was a time when Zambales was an island 

 and the sea reached from Manila Bay to the Gulf of Lingayen. Volcanic 

 eruptions accompanied the displacement, strong and still active in the 

 southern part (Taal Volcano), weak and extinct in the interior (Arayat). 



The upheaval which lifted the whole western coast of Luzon out of 

 the sea also laid the central plain dry and the two bays to the northward 

 and to the southward are the remnants of the former connection. 



If we look for a similar occurrence in other pai'ts of the world, we 

 find one in the Ehine Valley between the Vosges and the Black Forest. 

 Here we have on both sides old granite and gneiss formations ; leaning 

 against them, and broken off in steps, lie sediments ; and between the two 

 ranges is the valley, with diluvial and alluvial deposits. Like Arayat, 

 the Kaiserstuhl, a volcanic mountain, rises from the plain abruptly and 

 without apparent connection with its surroundings. To prove this theory 

 a careful study of the boundary line between the plain and the mountains 

 will be required. If we find the youngest sediment beds along this line 

 dipping from east, north and west toward the plain, and if we find them 

 rising not regularly but in steps separated by fissures from each other, we 

 can safely say that this theory is well foimded and corresponds with the 

 facts in the field. 



