83 
191 5 — 1 6 . ] The Origin of Oil-Shale. 
The residues in A, B, and C are paraffin, in D asphalt, hence the high 
specific gravity. D was selected on account of the percentages of the 
kerosene and lubricating fractions being nearly the same as those of 
A, B, and C. The analyses have been somewhat simplified to enable the 
comparison to be made easily. The high percentages of naphtha in the 
crude petroleums distinguish them at once from the distilled oils. 
The beautiful freestones of the Oil-Shale group probably owe their 
economic value, their comparative lack of hard cementing material, and the 
absence of plant remains except as mere casts of tree trunks, to having 
been at one time oil-sands. No geologist who has studied petroleum can 
examine such freestones without comparing them mentally with oil-rocks, 
and thinking how admirably they are adapted for forming underground 
reservoirs of petroleum. 
The abnormal deposit known as Torbanehill mineral or torbanite 
deserves special mention, as it differs in several particulars from ordinary 
oil-shale, and as it has been the subject of much interesting research 
and some famous lawsuits. It is the highest in the geological series of 
all the oil-shales, the lowest in specific gravity, and the richest in yield 
of oil. 
It is described as being “ of a brown or nearly black colour, having a 
yellow or fawn-coloured streak, without lustre, and subconchoidal fracture. 
It shows parallel banding by splitting, and, although homogeneous in 
appearance in the fresh state, shows stratification when spent in the 
retort. It is non-electric. It is a mass of carbonaceous matter without 
structure, mingled with stems or roots of trees showing structure, and 
the fossils were found throughout the bed and not merely on the surfaces 
of seams.” * 
The yield of oil ran as high as 130 gallons per ton, but the yield of 
ammonium sulphate was small. 
The deposit having been worked out, it is difficult to obtain accurate 
details of the field relations ; but owing to the legal controversy upon the, 
question as to whether Torbanehill mineral could be classed as a coal or 
not, many notes of interest are preserved. The seam mined near Bathgate 
in Linlithgowshire occurs just above the Sandstone group correlated with 
the Millstone Grit horizon in England. The thickness usually varied between 
18 and 20 inches, and the deposit lies on fireclay and is overlaid by bituminous 
shales and occasionally blackband ironstone. The seam passes laterally 
into coal or black shale. 
* Oil-Shales of the Lothians , p. 160 . 
