324 SMITH. 



Other quartz diorites have been encountered in Batangas (Loboo 

 Mountains), in Masbate, in Lepanto and elsewhere. 



Metamorphic rocks. — These are found in isolated patches in many 

 portions of the Archipelago, and are naturally to be seen in or flanking 

 the mountainous areas. Some are derived from igneous rocks and some 

 from the sedimentaries. Their age is uncertain, many undoubtedly are 

 Tertiary. That any of them are Archean is extremely doubtful. There 

 is absolutely no reason now for supposing any of those at present 

 known or as yet to be discovered to be as old as the Archean. 



We have serpentines, amphibolites, and magnetite schists in Ilocos 

 Norte. In Eomblon, marble and mica schists are found. The marble 

 is metamorphosed limestone, and in all probability the mica schists were 

 derived from Tertiary sandstones and shales. Some schists of unknown 

 origin occur in Cebu on the flanks of the cordillera. In the lower 

 Zamboanga Peninsula there is a considerable exposure of quartz-sericite 

 schists which may represent metamorphosed sediments, although I am 

 not certain of this. In Ambos Camarines we have gneissic granite, 

 schistose diorite, slaty shales, and brecciated sandstones. In my opinion, 

 we can argue nothing in regard to age from the presence of schists. 

 Metamorphics are products of dynamism and may be of any age. 



Owing to lack of space and to the fact that I have described several of 

 the Philippine schistose rocks elsewhere, 17 I shall not go into greater 

 detail at this time. 



3. Metad writes. — The metadiorites include a number of rocks in which 

 the hornblendes are not primary, but secondary. They are derived from 

 holocrystalline rocks containing pyroxene. 



4. Pyroxenite . — Bare, brownish and rocky hills having scattered white 

 patches of efflorescence occur in many parts of the Islands. Such hills 

 usually are composed of pyroxenite, passing in places to peridotite, and 

 where altered it is a serpentine. The efflorescence is magnesite (magne- 

 sium carbonate) derived from the decomposition of the ferromagnesian 

 minerals in the rock. This rock is almost black, inclined to greenish 

 where passing into serpentine, and is very hard and dense. I have noted 

 great areas of this formation in Ambos Camarines, Batan Island, Albay, 

 and Ilocos Norte. There is usually an accumulation of iron ore associated 

 with this formation. 



5. G-abbros. — These rocks may be thought of as having cooled too 

 slowly to form basalts. They stand in the same relation to basalts as 

 do diorites to andesites. This generic relationship of the coarser rocks 

 and the extrusive lavas in this region in one of the first things to under- 

 stand clearly. The great feature of the quantitative classification is that 



17 The Asbestos and Manganese Deposits, etc., of Ilocos Norte. This Journal, 

 Sec. A (1907), 2, 145. 



