75 
1915-16.] The Origin of Oil-Shale. 
The first point to be noted is the high percentage of water in the fuller’s 
earth as compared with the shales or brick clays, while the spent shale 
naturally contains little or none. 
The next point of importance is that, though the silica percentage does 
not differ very greatly, nor the alumina percentage, the calcium percentages 
are lower in the fuller’s earth and the alkalis higher than in the brick 
clays and shales. This seems to hold good in all cases. The spent shale 
has lost most of the alkalis in the burning. But otherwise it is evident 
that in composition it approximates more nearly to fuller’s earth than 
to brick-clays or ordinary shales 
The researches of Mr H. E. Ashley ( American Ceramic Society, vol. xii) 
point to the facts that the absorptive capacity of a clay depends more upon 
its colloid contents than on its actual chemical composition, and that fuller’s 
earth is very rich in colloids. The amount of colloids, however, seems to 
depend largely on the percentage of alkalis present, and possibly also on 
the percentage of alumina, so that chemical composition cannot be ignored. 
Addition of lime to a clay seems to destroy the colloids, and hence we find 
that a clay rich in lime is poor in absorptive capacity. 
Much additional research would no doubt be required to establish these 
points beyond the possibility of doubt, but so far as the evidence is avail- 
able we may conclude that the clays or shales most capable of absorbing 
and adsorbing inspissated petroleum must be low in specific gravity, fairly 
rich in alkalis and alumina, poor in lime, not very rich in magnesium 
and iron. 
These characteristics are typical of the inorganic matter of oil-shales. 
In the richest variety of oil-shale, torbanite, we find that the percentage of 
alumina is very high, and those of iron and magnesia exceptionally low. 
We may therefore accept the proposition that the colloid content of a 
shale is the determining factor as to whether, given the necessary conditions 
and the supply of inspissated petroleum, it is capable of becoming an oil- 
shale or not. 
That a shale or day may be absorptive and adsorptive enough to con- 
tain a sufficient percentage of hydrocarbons to become a rich oil-shale can 
hardly be doubted. Quite apart from the absorptive and adsorptive pro- 
perties of fuller’s earth in its ordinary state, the removal of hygroscopic 
water amounting to anything between 12 and 24 per cent, of the weight of 
the rock would admit of the taking up of an approximately equal weight 
of inspissated hydrocarbons. Where a series contains both oil and water 
it is usual to find them more or less completely separated, the water 
impregnating certain beds or bands and the oil others. When the oil is 
