11 
my visit it still held a considerable quantity of crude oil, even though the works had been idle tor 
a long time. Mr. Fell tells me that when the Wolgan River is very high this tank fills with water 
and overflows, so that large quantities of crude oil run down stream. After such an occasion the 
occurrences of crude, oil should be very plentiful down the course of the Hawkesbuiy River. 
With regard to the small, sometimes microscopic, showings referred to in connexion with 
some of the boring operations. 1 have pointed out in my Queensland report* * * § that there is always 
a suspicion that such small quantities have been derived from the plant used for drilling, and 
showed that the quantity of oil found in the muds used for flushing the rotary bore at Orollo 
closely corresponded with that found in other bores, although in the first case the oil was 
undoubtedly derived from the drilling plant. Thus we have no positive evidence of the occurrence 
of seepages, which are beyond suspicion in this area. Again, in my Queensland report. I have 
dealt with the statement that oil-field areas are known in America, where no seepages occur, j 
This is so, but the conditions are totally different. In very few parts of the world have the strata 
been so little disturbed as they are in some oil-field areas in the United States. Even the older 
Palaeozoic rocks have been so little metamorphosed that oil and gas are obtained from them at 
manv places. Moreover, in most of such cases, beds of the same age as those underlying the 
surface in these areas where no seepages exist, h ve already been proved to carry oil in other 
localities. However, let us put the matter another way. Let us suppose that a corked earthenware 
jar is badly cracked in several places and is lying on its side, and that a number ol men come that 
way looking for water which they know it formerly contained. The observant man will look at 
it. notice the jar has been badly cracked since the water was put in, the absence of any leakage 
of water from these cracks, and conclude that the jar is empty. The thoughtless person will not ice 
nothing but the jar, and will open it and expect to find it still full. The optimist will say Oh, 
well, the cracks are of no account ; they cannot have let the water out, and he, too, will open 
the jar, or he may try to sell it unopened to one of the others. The man who is thirsty and whose 
need is great may notice the cracks with some misgiving, but will open the jar on the chance that 
some water is still left in it. I am afraid that the general public can be divided into each of these 
classes, and in any case, Australia generally is in the case of the last man, and certainly most of 
the areas in the Sydney Basin correspond very closely with the simile of the cracked jar lying on 
its side, only there is no cork in the jar. The possible oil-bearing strata outcrop in many places. 
All their edges come to the surface, and yet no oil -impregnated beds have yet been discovered in 
them. 
6. The Carbon Ratio Theory as applied to the Permo-Carboniferous Deposits 
in the Sydney Basin. 
However, we will assume, as we are entitled to do, that some of the closed structures may 
contain oil or gas, and tackle the problem in another way. Again referring to my Queensland 
report, J 1 have discussed at some length therein the Carbon Ratio hypothesis. That is, the 
relation between the percentage of fixed carbon present in pure coals and the presence of petroleum 
supplies in neighbouring strata. The proportion of fixed carbon to volatile constituents, ash 
and water being excluded, stated on a percentage basis, is called the carbon ratio, and has been 
proved to be a measure of the amount of metamorphism that has taken place not only in the 
coals but in the adjacent strata. It has been found in American oil-fields that where the carbon 
ratio is from 50 to 55 the chances of finding oil are pretty certain. Where the ratio is from 55 
to 60 there is a chance of 1 in 10 in favour of finding oil in the strata. Where it exceeds 60 the 
chances are so very small that they can be pretty well neglected as a business proposition. 
Mr. Millard, with his usual thoroughness, obtained the results of numerous analyses of 
coals made by the Mines Department of New South Wales from samples taken from most of the 
collieries in the northern part of the Sydney Basin, and from these he worked out the carbon ratios. 
Subsequently he prepared a map showing the " isovolves v for the area. An " isovolve 77 or 
“ isocarb ” is a line drawn through points in an area where the carbon ratios are similar. It is. 
very like the 6 * isobars 57 shown on the weather charts in the newspapers, which are lines drawn 
through places where the barometric readings are similar. The map is published with his article, 
already quoted .§ The isovolve for a carbon ratio of 50 takes in that part of the Lochinvar Dome 
around Branxton. The 55 isovolve coincides pretty closely with the outcrop of the Greta Coal 
Measures, save in the west, where it runs off through Singleton and Muswellbrook. The 60 isovolve 
is shown running from a point near Seaham to the east of Maitland and round to the neighbourhood 
of Newnes, where it terminates against the Lower Palaeozoic rocks. Then comes 65 to the 
south of the Newcastle coal-field area, while 70 and 75 are shown running through the deeper 
part of the Basin in the neighbourhood of Sydney. 
* Loc. cit. pp. 24-25. 
t Loc. <?it. p. 'I'l. 
x Loc. cit. p. 7. 
§ Loc. cit. p. 160. 
