422 The Philippine Journal of Science 1923 



DIORITE 



The best exposures of diorite in the Baguio region occur in 

 Antamok Valley and vicinity (Plates 1 and 2). Iddings, 8 in 

 describing a sample from Antamok Valley, says: 



At Antamok, Benguet Province, there is medium-grained quartz-diorite, 

 with inequi granular consertal fabric. It consists of plagioclase and 

 considerable brownish-green hornblende, anhedral with respect to each other, 

 but euhedral toward quartz and orthoclase. There is some altered biotite. 

 In places the orthoclase is intersertal to poikilitic, with inclusions of 

 plagioclase and hornblende. 



Diorites frequently associated with schists commonly compose 

 a part of the basement complex upon which sedimentary rocks 

 of the Vigo group of Miocene age were deposited. In many 

 places fragments of diorite compose the sandstone of Vigo age 

 and occasionally the sandstones are decidedly arkosic. The 

 abundance of feldspar, hornblende, and quartz grains in the 

 Vigo sandstones is in sharp contrast with their absence or rare 

 occurrence in the sandstones of Malumbang Pliocene age. 



VIGO GROUP, MIOCENE AND ] 



Six kilometers west of Baguio City Hall and 400 meters south 

 of the Naguilian Road at an elevation of 1,095 meters (3,650 

 feet, aneroid) a dark gray, argillaceous sandstone which 

 weathers to a tan clayey sandstone occurs (Plate 2) . Embedded 

 in this sandstone are numerous specimens of Vicarya callosa 

 Jenkins and coral fragments. The strike is approximately east 

 and west, with a dip of 35° south. These sandstones without 

 much doubt are unconformably below the Malumbang forma- 

 tion, as the dip is greater and the strike observations taken in 

 the Vigo of this vicinity indicate that the Vigo group was 

 faulted and folded along different axes than the gently inclined, 

 westerly dipping limestones exposed along the Naguilian Road 

 between kilometer posts 4 and 5. In this vicinity the dip in the 

 coralline limestone, as Plate 5 clearly shows, is but 10°. The 

 following species were collected at locality 40x: 



Astreopora cf. myriophthalma Cerithium bandongensis K. Mar- 

 Lamarck, tin. 



Fungia cf. decipiens (K. Mar- Conus sp. 



tin). Cyprsea sp. 



Madrepora duncani Reuss. Natica sp. 



Area sp. Vicarya callosa Jenkins. 



