8 
In both northern and southern areas each of the coal-bearing stages has been seriously 
affected in places by volcanic intrusions. In dealing with L ' The Coal Resources of New South 
Wales,”* the Government Geologists state that " The Greta Coal Measures in the northern part 
of the State have been intruded by granites and quartz-f&lsites, which have destroyed a Considerable 
proportion of the coal, and in all parts of the main coal basin the Upper Coal Measures have been 
intersected by intrusive dykes, though their effect upon the coal is more noticeable in some cases 
than in others, and cases are given where Upper and Middle Coal Measure seams were converted 
into natural coke or completely cindered. It is also stated that “ It is in the Southern coal-field 
however, that the greatest effect of intrusion upon the coal seams is noticeable, and “ that large 
areas have been converted into natural coke." 
If oil is to be found then even in the Permo-Carboniferous Strata it must be limited to 
the Upper or Lower Marine Series, and especially where these deposits attain their maximum 
development in the Hunter River area which, so far as can be ascertained, is the only area in 
which the full sequence of the Permo-Carboniferous System is present. Considerable thinning 
of certain horizons appears to take place to the south and west of the Hunter River area. The 
Lower Marine Series make no appearance on the southern and western margins, while the Upper 
Marine, so far as is known, consist solely of conglomerates on the western rim, where it rests 
directly upon a contorted series of Devonian age. while a series of volcanic lavas and tuffs, over 
1,700 feet in thickness, form the upper portion of the Upper Marine Series, and come immediately 
below the Upper Coal Measures in the southern area. Below these volcanic beds come 3,000 
feet of deposits containing marine fossils and consisting of tuffaceous shales, grits, sandstones, 
and conglomerates, which also belong to the Upper Marine period. 
3. Structural Features Considered with regard to Oil. 
As previously stated, the Permo-Carboniferous rocks form a basin which covers a very 
extensive area around Sydney. As a rule the beds dip at very low angles towards the centre of 
the depression, and there is an absence of the kind of folding that is necessary for the accumulation 
of petroleum, excepting in one or two areas towards the margins, where on the other hand the beds 
have been seriously fractured and faulted, the displacement of broken blocks being sometimes 
very considerable. The top of the coal measures lies at a depth of nearly 3,000 feet below Sydney, 
which is near the lowest part of the basin, an upper seam being worked at Balmain, on the Harbour 
frontage. What may be present below this depth can only be surmised. The centre of a synclinal 
depression of this nature is quite unfavorable for the accumulation of oil, so attention must be 
confined to the marginal areas where the beds are uplifted, and especially to those areas where 
uplift has been accompanied by folding. One such folded area occurs to the west of Penrith 
and Richmond, towards the western rim of the Basin. Here a sharp monoclinal fold affects both 
the Triassic and Permo-Carboniferous rocks. A monoclinal fold of this character is not 
unfavorable to the accumulation of oil. especially if it be terraced, and some closure of the terraced 
structures can be indicated bv detailed geological work, and, moreover, if other necessary factors 
are present, I am unable to discover that any such work has been carried out or that any closed 
geological structure has been found. However, some drilling for oil has been done in this vicinity, 
one bore, reaching a depth of 2,700 feet, but the results were entirely disappointing. The reasons 
for failure are well set out in the bulletin by Mr. Leo J. Jones already cited.f 
In any case to bore through the Triassic and Permo-Carboniferous Coal Measures in order 
to test the underlying Marine Series, i.e., to a depth possibly of over 4,000 feet, would be a great 
waste of energy when the sa me beds can be tested elsewhere and under more favorable conditions 
without the necessity for drilling through any overlying cover whatsoever. 
Due west of the Penrith area and on the uplift side of this monoclinal fold, at an elevation 
of 3,263 feet above sea level, a bore was put down by Mr. John Fell’s Company at Hartley Vale 
to test for the presence of kerosene shale. This bore is said to have ended in the Upper Marine 
Series at a depth of 1,366 feet, but found no traces of petroleum. 
The most suitable geological structures for the accumulation and retention of petroleum 
that 1 have been able to discover in this region occur on the northern rim in the Hunter River area. 
Professor Sir T. V . Edgeworth David has shown that this northern margin has been subjected 
to stresses which have produced both folding and faulting on a considerable scale, and his detailed 
map shows at least one closed or partly-closed structure, the Lochinvar Dorne.J Mr. H. C. 
Millard. Geologist for the Hunter River Oil Company, has, during the past two years, made a 
careful study of this area, adopting up-to-date oil-field methods. By running structural contour 
lines on a definite geological horizon, he has clearly defined the structure and the nature of the 
closure. The Lochinvar Dome is very badly fractured in places, faults displacing the strata 
* Bulletin No. 6, by the StiUf of the Geoherien! Survey, pp. 23 24. -Department. of Mines, (Jcol. Sttrv., Sydney, 1924. 
t Loe. i it. pp. 25 33. 
L r The Geology of thr Tluutrr lUu Unui \b -u,. \ s.W. Memoirs of the Geoloizw.-jR Survey of N.S.W., .No. I, Sydney, 11107. 
