308 The Philippine Journal of Science ms 



between the pieces in the agglomerate, but apparently does not 

 occur as beds of exclusively fine-grained material. Part, at 

 least, of the ejecta from Isarog is water-laid, but the formation 

 is not bedded at any of the observed exposures. The series 

 extends to the north as a veneer of gradually diminishing thick- 

 ness over the metamorphic rocks. 



Isarog Volcano belongs to a period older than the volcanic 

 peaks to the south of it in Albay, one of which, Mount Mayon, 

 is still active. It is probably younger than the tuffs and flows 

 on the north coast of Caramoan, inasmuch as the latter are 

 interbedded in part with the upper beds of the Tertiary sedi- 

 mentaries, while the original distribution of the material from 

 Isarog appears to have been influenced somewhat by the existing 

 topography. 



PLIOCENE TUFFS, FLOWS, AND AGGLOMERATES 



The tuffs, flows, and agglomerates in the northern part of 

 the peninsula are distinguished from the Isarog formation 

 because of their probably greater age, their different character, 

 and the complete segregation of the two formations in distri- 

 bution. The northern series of volcanics consists of compact, 

 perfectly bedded tuffs, tuff-sandstones, and intercalated, sheet- 

 like flows, all of which are andesitic in character. In the region 

 of the contact between this formation and the sedimentaries 

 at the eastern end of the peninsula there are beds of limestone 

 containing fragments of tuff in a series of strata which have also 

 been pierced by domelike or pluglike intrusions of andesite and 

 andesite-agglomerate. The series of tuffs, flows, and agglom- 

 erates is at least 100 meters thick. It lies nearly horizontal 

 and forms low, grass-covered hills along the coast, but extends 

 inland only to the base of the mountains. 



TERTIARY SEDIMENTARIES 



The sedimentary rocks in eastern Caramoan are a succession 

 of limestones, shales, conglomerates, and fragmental or clastic 

 sandstones. A single thin bed of coal is intercalated with the 

 shales and sandstones. The thickness of the sedimentary series 

 is undoubtedly not uniform, because the beds overlap progres- 

 sively on the basal formation. However, the maximum thick- 

 ness must be more than 500 meters. Intrusions of andesite 

 and andesite-agglomerate have pierced the sedimentaries north 

 of the town of Caramoan and again at Palag (or Apatag, as 

 the name is rendered locally) Bay. The strike of the strata 

 varies from north-northeast in the northern and western parts 

 of the sedimentary area to west-northwest farther southeast; 



