MINERAL RESOURCES OF AROROY DISTRICT. 409 



The magnetite is not very prominent, although several large grains 

 occur. It is generally, though not always, associated with the augite. 



The ground-mass is largely made up of indistinguisliable alteration 

 products, probably resulting both from the decomposition of the feldspar 

 and the devitrification of the glassy base. However, in parts of the 

 slides there seems to be a dark, greenish glass containing minute black 

 rods. These rods are extremely fine and narrow, and, although occurring 

 in greater numbers around the edges of the augite and less prominently 

 about the leueite phenocrysts, form an irregular, branching network 

 throughout the ground-mass. Possibly these are skeleton crystals of 

 magnetite. 



The occurrence of this potash rock among the andesites and basalts 

 of this district is most unusual, and all the more so as it is the only 

 leucite-bearing rock known in the Philippines or Japan. Behrens ^* has 

 described similar rocks from Java. 



The outcrops in the vicinity of the leueite tephrite are all of andesite 

 agglomerate and it seems probable that the rock occurs as a dike cutting 

 the agglomerate. This is all the more likely as the dike already described 

 as cutting the sediments on the Gold Bug claim seems to be of similar 

 type, though much decomjDOsed and without recognizable leueite. 



While the evidence is too doubtful to make advisable any definite 

 statement, the sequence in the Panique series seems to have been as 

 follows : The hornblende andesite probably is the earliest and the mass 

 of Mount Vil-lon is intrusive, although it is uncertain whether the 

 rock forming the hills north of the Lanang Eiver is intrusive or effusive. 

 The larger hills between Kalakbao Hill and Panique Creek and including 

 Panique Hill are augite andesite and may represent the stocks of the 

 volcanoes from which issued the mass of pyi"oclastic material which 

 to-day covers such a large part of the area. Periods of quiescence 

 during the volcanic activity are marked hj the sediments found in 

 Panique Creek and on the Gold Bug claim. The basalts found in 

 various parts of the area probably are later than the andesite, and the 

 youngest rocks of the series are almost certainly the leueite tephrite and 

 the related dike, cutting the Gold Bug sediments. 



The Mountain Maid limestone. — On a small southerly spur of Mount 

 Bagadilla, just at the eastern end of the gorge of the Guinobatan Eiver, 

 at an elevation of about 150 meters, is a small outcrop of a dark blue 

 limestone, similar to that found in places along the main range of the 

 island. Dr. Warren D. Smith, who has examined thin sections of 

 this rock, considers it to be of Middle Miocene age. Thick jungle 

 surrounds the outcrop, and the field relations consequently are uncertain. 



" Beitraege zur Petrographie des indisclien Archipels. Natuur. Verh. d. Koninkl. 

 Akad. Leiden (1880), 23, 38, 58. 



