Reviews — M. Stewart — Sedimentary Oil Deposits. 571 



had much opportunity of studying the occurrence of oil in the field. 

 He here puts forward an interesting theory concerning the origin 

 of oil. 



Commencing with a statement in favour of organic origin, he 

 proceeds to discuss the well-known but unexplained property 

 possessed by clay whereby it is able to absorb oil and hold it under 

 water. Several interesting quantitative experiments were performed, 

 and it was found on shaking up clay and water and adding oil that 

 66 grammes of clay sediment took dovpn with it on settling all the 

 oil up to the amount of 14 c.c. The clay and oil used were both 

 from the Yenangyoung Oilfield of Burma. When an American oil, 

 much ligliter and of much less viscosity, was used a still greater 

 absorption occurred. 



Microscopic examination of the oily sediment showed that the oil 

 was not imprisoned as oily films upon the grains, but " was merely 

 mechanically mixed with the sediment, and that it was the small size 

 of the shale particles that made it impossible for the globules of oil to 

 escape between them and so reach the surface". The limit to the 

 quantity of oil which can be held is reached " when the pei'centage 

 of oil globules in the whole mass of particles is so great that the oil 

 globules are almost in contact ". This varies with the size of the 

 globules, which in turn is dependent on the viscosity. 



" The deposition of oil is purely a matter of gravitation." The 

 oil becomes mechanically mixed with the sediment in the form of 

 globules. The oil is unable to separate out, because it is not miscible 

 with the wet mud particles, which part them and prevent them from 

 coalescing. 



" The mixture of sediment and oil, being still of higher specific 

 gravity than the water, falls to the bottom and is deposited as 

 a sedimentary deposit." 



We think Dr. Stewart's explanation of the absorption of oil far 

 preferable to those put forward hitherto wherein some mysterious 

 affinity between oil and clay was assumed ; but we think that the 

 physicists could throw still further light on the problem, and that 

 the question of whether shale pai-ticles would be coated by oil under 

 water, or whether globules of oil would be coated with specks of 

 shale, or whether the globules become merely mechanically im- 

 prisoned, may be dependent upon the various surface tensions between 

 the liquids and solid concerned. Some readers probably will consider 

 that flowing water would have to be unusually highly charged with 

 mud for oil to be carried down in the manner described. 



In the later pages of the pamphlet it is suggested that in oil- 

 bearing formations " oil is of sedimentary origin and is not a 

 secondary product in deposits"; the decomposition of the organic 

 matter (mainly vegetable) has occurred in closed lagoons and swamps 

 " under bacterial action, the oils so formed rising to the surface and 

 forming a layer of oil ". At times the oil would find its way into 

 the rivers and ultimately would be deposited in the manner described 

 above. Later, as other strata accumulated above, a certain pressure 

 would be reached for each bed of clay, when the oil would be 

 squeezed out and would find its way into the seam of sand lying next 



