X, A, 5 Pratt: Reconnaissance in Caramoan Peninsula 313 



On the western end of the peninsula, bordering San Miguel 

 Bay, there is an area of light-colored schistose porphyry, which 

 was identified as schistose andesite by Smith.** This rock is 

 grouped with the basal igneous complex in this preliminary 

 study, but there is no certainty that it is as old as the basal rocks. 



CORRELATION 



Mount Isarog is one of the older of the extinct volcanoes in 

 the Philippines. Mount Mariveles, near Manila, is usually taken 

 as the type of these older volcanoes, the lavas of which were 

 more siliceous than the ejecta from the subsequently active 

 volcanic centers. The activity of Mount Mariveles, according to 

 Smith, ^ began in Pliocene time and continued into the Pleistocene ; 

 a corresponding age may be assigned to the Isarog ejecta. 



The tuffs, flows, and agglomerates on the northern coast 

 appear to be in some degree contemporaneous with the upper 

 part of the Tertiary sedimentaries, assuming that the tuff 

 observed in the limestone beds near the top of that series is 

 related in origin to the tuflf of the volcanic formation. In Cebu 

 there are tuffs and flows immediately beneath the limestone, 

 which Abella ^ flxed as Post-Pliocene. Tuffs, flows, and ag- 

 glomerates similar in appearance to those in Caramoan and 

 probably of corresponding age are found in the Laguna de Bay 

 region east of Manila. Without much question these various 

 occurrences may be correlated and placed in the Pliocene or 

 upper Miocene. 



The upper part of the sedimentary series corresponds roughly 

 with the limestone, sandy limestone, and clay-tuff at the top 

 of the sedimentary rocks in the petroleum fields of Tayabas and 

 Leyte.^ The work in Tayabas fixed this general horizon as upper 

 Miocene and Pliocene. The shales and associated rocks in the 

 lower part of the sedimentaries may be correlated directly with 

 similar rocks elsewhere. The coal horizon and the underlying 

 thin-bedded shale are recognized characteristics of the Philippine 

 Tertiary. In the basal limestone of the Cebu series I found 

 fossils which Smith ^° identified as Heterostegina margay^ita 



" Dr. Warren D. Smith made a petrographic study of the rocks collected 

 during the field work for the reconnaissance of southeastern Luzon, which 

 included this rock. 



' This Journal, Sec. A (1913), 8, 235 et seq. 



' Abella y Casariego, Enrique. La Isla de Cebu. Imprenta y Fundicion 

 de Manuel Tello, Madrid (1886), 120. 



"This Journal, Sec. A (1913), 8, 301 et seq. Ibid. (1915), 10, 241. 



"Ibid. (1914), 9, 157. 



