viii, a, 5 Pratt and Smith: Petroleum Resources 363 



The refining or fractionation of petroleum by diffusion through 

 porous media is well known, and the characteristic clarified or 

 refined appearance of Tayabas oil might be so explained. It 

 has been shown 21 experimentally that the diffusion of petroleum 

 through porous media exercises also a selective function by which 

 the unsaturated hydrocarbons are removed. The Tayabas 

 petroleum has a moderately high content (30 per cent) of 

 unsaturated hydrocarbons, the presence of which would seem to 

 dispute the theory that the petroleum had been subjected to the 

 refining effect of diffusion. However, a discussion of the origin 

 of the petroleum in the oil fields of Kansas 22 quotes Dr. David 

 T. Day in an expression of the belief that the Kansas petroleum 

 shows the effects of diffusion, while according to the same 

 authority 23 Kansas petroleums contain from 12 to 50 per 

 cent of unsaturated hydrocarbons. Apparently, therefore, the 

 presence of unsaturated hydrocarbons in the Tayabas oil is not 

 incompatible with the theory that the oil has been refined by 

 diffusion. 



If the Tayabas petroleum has been refined by diffusion, 

 the diffusion may have been either a lateral migration through 

 the Bacau stage or a migration upward or downward from the 

 neighboring strata. -The formations exposed at the surface 

 above the Bacau stage show no indication of oil. If the oil was 

 ever present in these beds, the greater part of it must have 

 escaped from their truncated edges along the anticlines. The 

 Canguinsa sandstone is locally of such fine-grained and compact 

 texture that it should retain traces of petroleum just as the 

 shale in the Bacau stage does, if petroleum had originated in, 

 or moved through, it. Apparently there is little chance that 

 petroleum occurs in the formations above the Vigo shale. 



It is possible that concealed members of the Vigo shale beneath 

 the overlapping Canguinsa sandstone are petroliferous, and that 

 petroleum from them migrates along the unconformity to the 

 Bacau stage, which often appears at the surface immediately 

 below the Canguinsa sandstone. If the petroleum were coming 

 to the Bacau stage along the unconformity, it would be expected 

 that the base of the Canguinsa sandstone would be most strongly 

 petroliferous. This is not the case; usually, the petroleum ap- 

 pears in the beds of the Bacau stage and not along the uncon- 

 formity. Moreover, in some places the Canguinsa sandstone 



21 Gilpin, J. E., and Cram, M. P., Bull. U. S. Geol. Surv. (1908), 365. 



22 Univ. Geol. Surv. of Kansas (1908), 9, 191. 



23 Day, David T., Bull. U. S. Geol. Surv. (1908), 381, pt. 2, 22. 



