55 
1915-16.] The Origin of Oil-Shale. 
To sum up the special characteristics of the Scottish oil-shale fields to 
which attention is called, the points to be noted are : — 
(1) The stratigraphical relations of the oil-shale fields to the coal-fields. 
(2) The fact that oil-shales are a special and not a universal feature of 
the stratigraphical horizons on which they occur. 
(3) The general and the minor structures of the oil-shale areas, the 
seams occurring in nutidinal areas, and on the crests and flanks of minor 
anticlines. 
(4) The decrease in richness of shales with depth in certain cases, i.e. 
down the flanks of the flexures. 
(5) Association of oil-shales with argillaceous deposits, especially as 
roofs to the seams. 
(6) The passage of oil-shales into normal carbonaceous shales. 
(7) The association of oil-shales in certain cases with phenomena char- 
acteristic of oil-fields. 
It is now necessary to turn to other countries to glean evidence as 
to the nature of oil-shales and their stratigraphical relations. For this 
purpose it is proposed not to consider all known occurrences of oil-shale, 
but to select certain countries and areas where the writer has had special 
facilities for observation. 
2. South Africa . — In the Karoo system, of Permian to Jurassic age, there 
are numerous seams of what under our definition must be classed as oil- 
shale. They occur chiefly in the eastern Transvaal and Natal in what 
is known as the Stormberg series, near the top of the Karoo system and 
beneath the great volcanic beds of the Drakensberg. 
The Karoo system has been variously estimated at from 15,000 to 19,300 
feet thick, the upper 4000 feet consisting of the volcanic beds of the 
Drakensberg. It is in the Stormberg series and in the uppermost beds of 
the Beaufort series that the well-known Coal Measures of the Transvaal, 
Natal, and Cape Colony occur, and within the confines of the coal-bearing 
territory oil-shales have been detected in many localities. The strata of the 
Karoo system in this region spread with almost perfect horizontality over 
thousands of square miles, but the plateau being deeply trenched by valleys 
and carved into great escarpments allows the series to be studied to great 
advantage. Dikes and sills of dolerite are numerous, but do not cause 
much disturbance of the bedding except merely locally. 
Speaking generally, the Stormberg series is of littoral type, and the 
rocks are chiefly arenaceous. The coal seams have usually both floors and 
