The previous articles on the subject do not emphasize sufficiently that cannel coals should not be used in 
preparing isoearb maps. Iff.hr. analyses of the runnel coals were used, the maps would lend to show areas of low fixed carbon 
content m the m jit ms where there teas much cannel coal. As these areas would not indicate regions of low regional alteration 
they would greatly detract from the value of the map. in fad , a map prepared in this way might lead one to believe that 
certain regions m which the carbon ratios were really too high for oil and gas were altered merely to the ideal degree , ami such 
a map ■ would be worst •. than nothing. 
The whole of this, and especially the last paragraph, might very well have been written to deal 
with the case- of the Greta coals. It describes and deals with the conditions exactly. At this 
point it would be well to find out just, how the coal samples were taken by officials of the New South 
Wales Mines Department for the preparation of the coal analyses from which we have been working. 
In Bulletin No. 6/ l: from which most of; the analyses were taken by myself, is the following 
statement : ” The method adopted in sampling was to cut out a strip of coal carefully with a pick 
for the whole thickness of the seam as worked so that the samples should represent the coal actually 
i-ent to market/ Oatmeloid portions of the coal are not excluded from the coals sent to market, 
so far as I have observed the coals trucked from the Greta area, and are, therefore, included in 
the samples taken. They form the best part of the coals, in any case, for gas-making purposes. 
The whole of the evidence makes it quite certain that 55.5 as an average carbon ratio for 
the Greta Series does not represent the true state of metamorphism in these beds, and, therefore, 
cannot be relied upon as any indication of the possibility of obtaining oil in this area. A 
considerably higher figure, probably between 60 and 65 at least, would, in my opinion, represent 
the degree of metamorphism which exists in the Greta Series. 
With regard to the occurrence of oil in this Kentucky region, Mr. Russell makes some 
interesting observations which may help in the consideration of our own areas. lie observes 
that (page 253) ** Nearly all the good od and gas production from sandstones and most of that 
from limestones lies below the 60 per cent, isoearb. The gas pools are for the most part located 
between the 60 per cent, and the 62.5 per cent, isocarbs. Moreover, in the case of most of the 
oil pools in sandstones above 60 per cent, the ratio of gas to oil is much greater than in the case 
of the oil pools in sandstones below the 60 per cent, isoearb. In the pools above 60 per cent, 
the production is quite “ spotted owing to the irregular porosity of the sandstones. Production 
in these pools consists for the most part in small wells scattered among gas wells and dry holes. 
The urea in the extreme eastern part of the State where the coals have a fixed carbon content 
greater than 62.5 per cent., is barren of oil or gas as yet.” These conclusions would cut out 
practically the whole of the Sydney Basin as possible oil-producing territory, but it gives us some 
hope with regard to natural gas. It agrees entirely with the opinions I have reached myself. 
Again, " It is noteworthy that in Kentucky as elsewhere, the coals are higher in fixed 
carbon in the anticlines than in the synclines/ This is important, for if we are to take the Greta 
Measures along wit h the upper and middle coal measures in dealing with carbon ratios, we should, 
apart from I he matter of \ he greater depth of the Greta, expect to find higher carbon ratios around 
the Lochinvai \nticline than in the synclinal basins on either side, whereas the reverse is the case. 
This again tends to show that the carbon ratios for the Greta coals do not represent the true facts. 
It also explains some of the low carbon ratios in certain areas which are local basins or synclines 
in the upper coal measures. Such low carbon ratios are to be found in the upper coal measures 
near Singleton, Hi\ s Greek, Muswellbrook. and Gunnedah in the north-western corner of the 
pernio- carboniferous area. Small structures undoubtedly exist in this part of the country which 
might be prospected, especially for gas. 
Mr. Russell, in a very important statement, shows that caution must be exercised in 
dealing with isocarbs. (Bage 255). While the isoearb map has an important use in predicting 
the best areas lor testing, il should be understood that it merely gives an indication of one of 
tin* conditions necessary for the occurrence of oil and gas. If source rocks and porous reservoirs 
are not present, there will, of course, be no production no matter how ideal the isocarbs are. On 
the other hand, if the isocarbs are extremely unfavorable, there should be no oil or gas 
production, even though the other favoring conditions are present." 
lie considers regions where the isocarbs are generally over 62.5 to be unfavorable in 
spite of the presence of good structures, thick source rocks and sandstones associated with them 
and another area which lies between the 60 per cent, and 62.5 per cent, isocarbs, he considers 
as only favorable lor testing lor gas. 
Finally, il will be instruct ive to quote from his conclusions (page 260) : 
I In certain n " i- >n uc|i as tin 1 eastern eoaklields of Kentucky, where the amounts of fixed carbon in the coal s 
vary greatly, regional average- rather than single analyses must be used in making isoearb maps. 
'1. Cannel coals and semi cannel coals should not be considered in making these maps. 
;>. In Kentucky there is a marked relation between the isocarbs and oil and gas production and the porosity of 
the sandstones. 
From the standpoint of the isocarbs alone, t lie best place for future testing is the portions of the western 
coxldield. which are well below GO per cent. 
Uy i In- Sin II of t lie 1 Oi'olo'iit'nl Survey, l)t«part.ir.«n( of Mint**. -Utul. Suiv., 1 1)2 -4 (? hl’Jo), p. a. 
• The ( nil • <>f N(»\\ South Wnlc 
