82 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Those clays with a sufficient colloid content readily absorbed the in- 
spissated products and gradually fixed them as kerogen, the porous sand- 
stones beneath supplying the material as long as the argillaceous rock 
could provide accommodation for it. 
In this connection two points may be noted : the occurrence of good 
porous sandstone beds not far beneath the most prolific oil-shales, and the 
occurrence of impervious shales above. 
It must also be understood that the shales may have contained the 
material to form petroleum originally, and this may have been inspissated 
and turned to kerogen in situ, but no shale could contain sufficient organic 
matter to form its full complement of kerogen, though it doubtless contained 
at one time crude unweathered oil to its full capacity. 
As the series became more open to weathering processes and lixiviation 
the sandstones would lose all traces of their former impregnation, but 
towards the crests of anticlines and minor flexures the process of inspissa- 
tion and absorption would survive longest, so that now the richest shales 
occur in anticlinal areas on the crests and flanks of flexures. 
Where an oil-shale passes gradually into a carbonaceous shale we have 
evidence of the transition stage between the petroliferous and the carbon- 
aceous phases. Where an oil-shale insensibly passes upwards or downwards 
into an unworkable bituminous shale it is evidence of either a lack of colloid 
content or a deficiency in the supply of inspissated petroleum. 
Finally, in a well-sealed anticline low in the series we find in the 
Broxburn district a remnant of the petroleum impregnation. That it is 
a true crude petroleum, though somewhat inspissated, and quite different 
from the oil distilled from the shales either artificially or naturally by 
the heat of igneous intrusions, is shown by the analysis : — 
A. 
B. 
C. 
D. 
Specific gravity 
•868 
•866 
•830 
•950 
Naphtha ..... 
3-5 
4-5 
10-2 
12-8 
Illuminating oil 
32-0 
36T 
34T 
36-0 
Lubricating oil . 
28*0 
25-6 
27-2 
32-0 
Solid residues .... 
11-0 
8-8 
12-5 
12*3 
Loss in refining 
25-5 
25-0 
160 
5-7 
Water ..... 
1-2 
100-0 
100-0 
100-0 
100-0 
A — Crude shale-oil (Broxburn). 
B — Naturally distilled oil from sill of igneous rock, Dunnet Mine (Broxburn). 
C — Crude petroleum from Sandhole Pit (Broxburn). 
D — Heavy inspissated oil from shallow boring near asphalt lake, Trinidad. 
