306 The Philippine Journal of Science 1915 



GENERAL GEOLOGY 



The greater part of Caramoan Peninsula consists of meta- 

 morphic rocks. Sedimentaries form the low-lying eastern end, 

 and volcanics occur along the northern coast, but the conclusion 

 that the central part of the peninsula is probably andesite, re- 

 corded in the reconnaissance already referred to, is in error. 

 The rocks have been grouped as follows in the probable order 

 of increasing age: 



1. Alluvial and littoral deposits. 



2. Isarog volcanic agglomerate and tuff. 



3. Pliocene tuffs, flows, and agglomerates. 



4. Tertiary sedimentaries j 



5. Metamorphic sedimentary rocks [ contemporaneous. 



6. Basal igneous complex. 



The distribution of these formations is indicated on the ac- 

 companying geologic map (fig. 2). 



ALLUVIAL AND LITTORAL DEPOSITS 



Alluvial plains are developed over limited areas along the 

 rivers at the town of Caramoan and the barrio of Parubcan. 

 A larger area of mixed alluvial and littoral deposits is encoun- 

 tered in the vicinity of Lagonoy. These deposits are composed 

 of surface detritus from the rocks of the various formations. 

 The alluvium at Caramoan is largely clay and sand from the 

 sedimentary series, while at Parubcan, where metamorphic rocks 

 have been degraded, there is a larger proportion of gravel. 

 At Lagonoy sand, clay, and gravel have been derived from the 

 volcanic tuffs and agglomerates flanking Mount Isarog. Pos- 

 sibly some of the fragmental volcanic ejecta was thrown out 

 late enough to have been interbedded with the recent alluvium. 

 In the northeastern and northern parts of the peninsula there 

 are mud flats largely covered at high tide, but there is little 

 alluvium above sea level. 



ISAROG TUFFS AND AGGLOMERATES 



Mount Isarog is clearly an extinct volcano from which both 

 flows and fragmental ejecta, uniformly andesitic in character, 

 have been extruded in the past. The flows and the fragments 

 in the agglomerates are porphyritic rocks with phenocrysts of 

 calcic feldspar in a brownish, pumiceous groundmass. Many of 

 the fragments in the agglomerate are partly rounded, so that 

 the rock is in part a conglomerate of volcanic materials rather 

 than a true volcanic agglomerate. The tuff, consisting of fine 

 fragments of the same character as the flows, forms a cement 



