57 
1915-16.] The Origin of Oil-Shale. 
Owing to overlap, in some districts the kerosene shale group forms the base 
of the series lying unconformably upon older rocks. Fresh- water, deltaic, 
and estuarine conditions are strongly marked in the shale group. 
The general geological structure is almost horizontal over a very large 
area. There are, however, gentle undulations with dips seldom exceeding 
a gradient of 80 or 90 feet per mile. 
In parts of the Capertee Valley, in Hartley Valley, and in several other 
localities the “ kerosene shales ” appear to be best developed towards the 
upper part of gentle monoclines and on the crests of the gentle undulations, 
and occasionally, though not always, decreasing or disappearing in the gentle 
troughs. 
The oil-shale is very closely associated with coal. Thus a seam fre- 
quently consists of a thin bed of impure coal at the base, a band of the 
shale, and another band of coal at the top. Fireclays, pipeclays, barren 
shales, and thin bands of ironstone occur above the shale seams, and the 
thickness of close-grained or impervious strata above the seams is often 
large. 
Such a section as the following is typical : — 
Cannel coal 
“ Kerosene shale ” 
Cannel coal 
“ Kerosene shale ” 
4 inches 
1 foot 8 „ 
3 „ 
2 feet 8^ inches. 
The workable shale seams are said to be lenticular, and they pass 
laterally into coals and earthy carbonaceous shales. 
The shale itself varies very greatly in quality. It is distinctly laminated, 
but has a conchoidal fracture, a brown or yellowish streak, and a distinct 
lustre. It resembles cannel coal in many particulars, and contains 
vegetable fossils. The richest varieties have a specific gravity as low as 
1*008 and a percentage of ash lower than 10, but the amount of inorganic 
matter is subject to great variations even in different parts of the same 
seam, and is as high as 56 per cent, in some instances. 
The yield of oil in the retorts is very high from the best shales, reaching 
as much as 160 gallons per ton, but the yield of ammonium sulphate is low 
as a rule. 
There is at least one case recorded of a shale having burnt at outcrop, 
a phenomenon usually associated with bituminous shales in oil-fields or with 
the transition stage between the petroliferous and carbonaceous phases. 
Thus it is seen that the New South Wales shale-fields have much in 
common with those of South Africa, both in geological structure and in the 
