X, A, 4 Pratt: Petroleum and Residual Bitumens 255 



still be a slight overlap on the limbs of steep folds, but the 

 structure as determined by the attitude of the upper beds must 

 be practically the same in the underlying, petroleum-bearing 

 Vigo shale. 



OCCURRENCE OF THE PETROLEUM AND RESIDUAL BITUMENS 



In Leyte petroleum is encountered at two places : namely, seep- 

 ing from the upturned edges of the Vigo shale and oozing from 

 the base of a hill which consists of a clayey tuff -sandstone belong- 

 ing to the Canguinsa. Residual bitumens occur in the Canguinsa 

 and in the Malumbang series; one questionable outcrop of solid 

 bitumen was observed in loose debris which appears to overlie 

 the Vigo shale, and a heavy, black oil or viscous bitumen was 

 found in sandstone near the base of the Vigo. 



The bitumens in the Canguinsa are encountered in five types 

 of deposits: (1) solid bitumens in lenses or pockets which tend 

 to follow bedding planes, but which also cross the bedding irreg- 

 ularly along fractures and cavities; (2) solid bitumens in reg- 

 ular fissures which penetrate the clay-tuff independently of 

 bedding planes; (3) in nonuniform mixtures of bitumen-impreg- 

 nated, clay-tuff fragments and subordinate solid bitumen; (4) 

 viscous or semiliquid bitumen-cementing breccias of flintlike lime- 

 stone, small domes of which protrude from the surface of the 

 clay-tuff formation; and (5) viscous or semisolid bitumen filling 

 the centers of hollow, cylindrical concretions which occur in the 

 clay tuff, with their longer axes nearly vertical and at right 

 angles to bedding planes. The bitumen in the Malumbang series 

 has impregnated porous limestone and sandstone, forming what 

 is known commercially as rock asphalt. The various occurrences 

 both of petroleum and of residual bitumen, which are indicated 

 on the map (fig. 2) by letter, will be described separately. 

 Chemical data on the petroleum and the bitumens will be found 

 in the discussion on the character of the bitumens. 



Outcrops A and B are jet black, lustrous bitumens with con- 

 choidal fracture, which have been mistaken by the Filipinos 

 who live in the vicinity for coal. The bitumen has a specific 

 gravity of 1.05, a black streak, and a hardness, at ordinary tem- 

 perature, of not more than 2. It melts readily, intumesces, and 

 flows imperfectly. Upon distillation it yields a delicate coke. 

 The outcrops have been on fire at various times, either through 

 spontaneous combustion or, more probably, through kindling 

 from the grass fires which sweep the region nearly every year, 

 and the clay surrounding them is baked to a red sinter at places. 

 Both deposits are found in Canguinsa clay-tuff at the base of 



