47 
1915-1916.] The Origin of Oil-Shale. 
action of water, etc., would remain. We can imagine a plant or plant organ 
decaying and leaving only the wax or fat that was originally meant for its 
protective covering, or perhaps some resinous excretion or secretion. But 
this would give us materials soluble in our solvents, and might account for 
the origin of petroleum or bitumen, but not for kerogen. 
“ Some shales are largely made up of entomostraca, and it is probable 
that the animal matter has in some cases been converted into kerogen. 
We can imagine kerogen being produced from any kind of organic matter 
by the action of microbes under special circumstances, the product being 
dependent on the microbe. Or, on the other hand, kerogen in some cases 
may be the remains of certain kinds of vegetable matter, like pine pollen 
or lycopod spores, perhaps little altered, the product being dependent on 
the nature of the original organic matter. 
“ As peat gives paraffin products on distillation very like those of shale, 
it is probable that shale contains ordinary vegetable or other organic matter 
that has undergone decay to substances of a humic acid nature, which have 
been rendered insoluble and preserved by chemical combination with the 
metallic oxides of the clay or water, the alumina, lime, etc. 
“ Oil-shale, therefore, may be composed of (1) vegetable matter which has 
been made into a pulp by maceration in water and preserved by combining 
with the salts in solution as already mentioned ; (2) richer material of many 
kinds, such as spores, which nature has provided with means of protection 
against decay ; and (3) a proportion of animal matter.” 
Comment upon this passage is hardly necessary: the accumulation of 
vegetable material in lagoons, especially such vegetable matter as leaves, 
may be observed in any favourable locality, but this hardly explains why a 
carbonaceous shale may be formed in one case and an oil-shale in another. 
There are some very fruitful suggestions in the quoted passage, but the 
proposition is left more “ suggested ” than “ proved.” 
Other suggestions as to the origin of kerogen need not be considered at 
length. Professor A. C. Seward and others incline to look towards fresh- 
water algae as the source of the organic matter, and suggest that a structure- 
less jelly-like mass might be formed by the decomposition of such organisms. 
Spores are also suggested, but the absence of resinous compounds in kerogen 
is against this, and Professor Seward even hints at the possibility of the 
carbonaceous matter having an inorganic origin. 
Mr de Salis suggests that the heat of intrusive rocks may have caused 
a natural distillation of hydrocarbons from bituminous seams in the Coal 
Measures, and that the distilled material may have collected in the shales. 
This theory is interesting since igneous rocks occur in the Scottish Oil-Shale 
