252 The Philippine Journal of Science 1915 



the Vigo, however, is not fissile and except for its darker color 

 resembles the overlying Canguinsa. It w^eathers into ellipsoids, 

 the forms of vv'hich stand out along the exposed edges of the 

 beds, with their major axes in the plane of the stratum. 



The Vigo shale is probably about 1,000 meters in maximum 

 thickness in Leyte, although complete sections were not observed. 

 Undoubtedly the thickness varies, because it is known to overlap, 

 unconformably, the formation upon which it rests. The most 

 extensive exposures lie to the east and south of Villaba, while 

 smaller outcrops are encountered at various places in the sur- 

 rounding country. 



Petroleum seeps from the Vigo at half a dozen places in Taya- 

 bas. Apparently it always comes from the upper part of the 

 formation. In Leyte two petroleum seeps were found in the 

 Vigo shale, and a very heavy, black, oil-liquid bitumen was 

 encountered in sandstone, closely above the basal complex upon 

 which the Vigo lies. The solid bitumens which occur in the 

 overlying Canguinsa were nowhere observed in the Vigo. 



INTRUSIVE ROCKS 



The intrusive rocks in Leyte are principally andesites and 

 andesite-breccias. Similar intrusions were observed in Taya- 

 bas, and the rocks of which they consist were described in 

 the report on that region. In Leyte the andesites are usually 

 porphyritic with phenocrysts of ferromagnesian minerals and 

 occasional calcic feldspars in a light-colored groundmass. Other 

 specimens are dark-colored, fine-grained, homogeneous rocks. 



A single outcrop of an igneous rock, which appears to be dio- 

 rite, is encountered at petroleum seepage I. This rock is some- 

 what decomposed, is holocrystalline in texture, and consists 

 essentially of calcic feldspars and hornblende or pyroxene. The 

 outcrop is at a low horizon in the Vigo shale and may represent a 

 part of the basal igneous complex instead of an intrusion. 



The intrusive nature of the andesites is indicated by their 

 relation to the strata in the surrounding sedimentaries ; by the 

 presence in at least two places of adjacent springs of warm 

 mineralized water which emits an odor of hydrogen sulphide; 

 by rare fragments of quartz, chert, and partly baked shale in 

 the rocks surrounding the intrusion; and in the case of the 

 Mount Tabeyta intrusion, by remnants of a calcite- and quartz- 

 cemented shale-breccia surmounting the andesite. 



The intrusions penetrate the Vigo shale and the Canguinsa 

 clay-tufl". Mount Tabeyta and the isolated conical hill at the 

 mouth of Campocpoc River are the largest and most conspicuous 



