54 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Geological Survey memoir is that as a general rule the yield of oil of a 
shale seam decreases with the depth. This is stated to be very marked in 
certain cases — e.g. in the Linlithgow district in the case of the Broxburn 
seam, — distinct but not so marked at Broxburn, and much less apparent 
at Oakbank. It is also stated that this decrease in yield with depth 
is most noticeable in the north, and less apparent towards the south. 
A series of laboratory results from analysis of samples from an incline 
on the Broxburn shale shows a decrease in the yield of gallons of oil per ton 
from 31*8 near the outcrop to 135 at a depth of something over 1000 feet. 
It is noted also that at a sharp bend or flexure in a seam the yield of oil often 
decreases. The possible cause of these phenomena will be dealt with later. 
One other characteristic of the Scottish shale-fields requires to be men- 
tioned, and that is the fact that evidence of crude petroleum is not wanting 
in the strata associated with oil-shales. Natural gas, liquid petroleum, 
elaterite, ozokerite, and albertite are all known in the shale-fields. The 
solid minerals usually occur in or near some intrusive igneous mass, where 
it can be proved that the heat of the intrusion has caused local distillation. 
In such cases cavities which may be in the solid igneous rock, within a 
fossil, or on joint faces may be found filled with liquid, plastic, or hard and 
solid hydrocarbons. Such occurrences are frequent where either coal-fields 
or shale-fields are invaded by intrusive igneous rocks — e.g. in the Karoo 
and in some parts of the Drakensberg in South Africa, — and they have no 
particular significance. 
But the facts that natural gas, odourless and combustible, has issued 
from boreholes in the Broxburn district, and that a constant oozing of 
petroleum and brine was encountered in the Sandhole Pit at a depth of 
some ten fathoms below the Dunnet Shale, are important. In this case the 
oil was collected for more than a year, and some 200 barrels were obtained. 
The oil had the green fluorescence so characteristic of natural petroleum, 
and a specific gravity of ’830. On analysis it yielded : — 
Petroleum spirit 10’2 
Kerosene 34 '1 
Lubricating oils ..... 27’2 
Solid paraffin 12-5 
Loss on analysis ..... 16’0 
This oil differs in some points from the oil distilled from the shales, 
notably in the percentage of petroleum spirit ; but in the high percentage 
of solid paraffin it resembles the shale-oil. The loss in analysis is un- 
fortunately very high, making it difficult to compare the oil with other 
crude petroleums. The oil being associated with brine is another link with 
normal oil-fieid conditions. 
