﻿BAGUIO MINERAL DISTRICT. 231 



Analysis of the limestone. 





Constituent. 



Per cent. 



Moisture ( — 110°) 



0.10 



Loss on ignition ( + 110°) 



42.49 



Silica (Si0 2 ) 



1.90 



Alumina (A1 2 3 ) 



1.72 



Ferric oxide (Fe,0 :1 ) 



.30 



Ferrous oxide ( FeO ) 



.04 



Calcium oxide (CaO) 



52.11 



Magnesium oxide (MgO) 



.97 



Potasium oxide (K 2 0) 



.07 



Sodium oxide (Na.O) 



.20 



Exposures of what arc undoubtedly pyroclastic rocks, now indurated 

 to a solid rock mass, occur in the immediate vicinity of Bagnio on the 

 rounded hills near the town. The best exposures of these are on the 

 Bagnio-Trinidad road, near Baguio. The rock is a purple-brown hard 

 and compact heterogeneous mass, to certain phases of which the name 

 "eruptive conglomerate" has been given in the field. The name expresses 

 the rock texture, which varies from a medium-grained variety to one 

 which is extraordinarily coarse. The material is entirely andesitic, and 

 two varieties of andesite are present, differing only in their groundmasses, 

 as evidenced chiefly by the color of the latter. In thin sections, the loose 

 texture of the rock is striking, being merely an aggregate of minerals, 

 all of the grains being more or less rounded. The minerals present are 

 the light-colored, monoclinic pyroxenes, hornblende, actinolite, plagio- 

 clase, magnetite and in areas, olivine, the tuff being in these localities 

 more basaltic than andesitic. The pyroxene is the most prominent 

 mineral, making up fully one-half the slides. It is greenish-yellow to 

 almost colorless in various sections, and not pleochroic. It is frag- 

 mentary, very irregular, generally rounded and shows prismatic cleavage. 



The feldspar is almost insignificant in amount, generally occurring in 

 small grains. Magnetite is present in large amount, being second only 

 to the pyroxene in abundance. The epidote which occasionally occurs 

 is idiomorphic and can readily be distinguished from either hornblende 

 or pyroxene by the marked basal parting. A microspherulitic structure 

 of feldspar, quartz (?), and magnetite is noteworthy, as is also the 

 intergrowth of feldspar and hornblende. 



This rock in addition to the Baguio outcrops, is very prominently 

 exposed on the road through the Pias Valley and on the Copper King 

 road near Loacan. Other exposures on the east side of the Antamok 



