332 The Philippine Journal of Science 1913 



The Bacau stage contains fewer beds of sandstone than the 

 Vigo shale proper, and the bedding planes are often less distinct ; 

 thus, exposures at Bacau and Sili have the appearance of massive 

 banks of compact, hardened clay, which are sandy in subordinate, 

 irregular zones only. To material of this character the ordinary 

 definition of shale which stipulates a fissile or laminated texture 

 does not apply strictly, but the term is convenient and, employed 

 in a broad sense, is preferable to "clay" or "clay-shale" in de- 

 scribing the rocks in the Bacau stage. The shale weathers into 

 concretion-like ellipsoidal pieces from which concentric layers 

 split off, and break into small fragments with conchoidal surfaces. 

 The manner of weathering distinguishes the petroliferous beds 

 from other fine-grained layers in the Vigo which are fissile and 

 split into flakes upon disintegration. 



Beds analogous in character to those in the Bacau stage are 

 found throughout the Vigo shale, but the Bacau stage proper 

 appears to be confined to a zone from 50 to 75 meters thick in 

 the upper portion. In the eastern half of the field, the Canguinsa 

 sandstone overlies the Bacau stage in a majority of exposures. 

 Occasionally (section on Dumalog Creek, Table XIII, page 333; 

 and on Bahay River, Table X, page 320), sandstone and fine 

 conglomerate, which are evidently a part of the Vigo series, 

 occur above the Bacau stage. In the western part of the penin- 

 sula sandy conglomerate is found near the top of the Vigo forma- 

 tion. These overlying beds may be always present above the 

 Bacau stage, but concealed generally by an overlap of the un- 

 conformable Canguinsa sandstone. The sandstone and conglom- 

 erate in the upper part of the Vigo shale are generally micaceous, 

 and show many carbonized leaf-impressions. In the south- 

 western part of the field, large pieces of silicified wood were ob- 

 served in the conglomerate, and on Bunsaua Creek a bed of 

 lignite 20 centimeters thick occurs in the shale below this horizon. 



Two exposures of andesitic agglomerate were encountered 

 which appear to be in the Vigo shale — one at the head of Tangob 

 Creek, north of Cabongahan, and the other on Dumalog Creek 

 at the head of Guinhalinan River. The Tangob exposure is 

 in the upper part of the series, a few meters below the Canguinsa 

 sandstone; while the outcrop on Dumalog Creek appears to be 

 considerably lower in the Vigo shale, several hundred meters 

 below the base of the Canguinsa sandstone. Elsewhere, no ag- 

 glomerate was noted except as float, and it is not certain that 

 the Dumalog agglomerate is in place. 



' The thickness of the Vigo shale is unknown. An apparent 

 thickness of about 1,400 meters is revealed in the Matataha 



