9 
present in it bv several thousands of feet. To the west, however. Mr. Millard found another 
dome of smaller area near the village of Belford which is practically unbroken .* * * § Professor David 
had already indicated anticlinal conditions in this vicinity, but it was left for Millard to prove 
the closure of the structure and its dome-like character. It is necessary to give both these 
structures, the Loch invar and the Belford Domes, very careful consideration, for undoubtedly 
they exhibit the most suitable structural features that 1 have seen so far during my investigations 
in Australia. 
4. The Lochinvar and Bin . ford Domes. 
The geological map accompanying this section of my Report gives an adequate idea of 
the nature of these two dome-like structures and the configuration of the outcropings of the beds 
which have been so folded. The map is based on Professor David’s map of the area, with two or 
three modifications. The oval line of outcrop of the Muree Beds around the Dome at Belford 
is based on Mr. Millard’s field work, and was checked in the field by myself. The swing round 
to the north-west of the Muree Beds in the outcrop west of Branxton, indicating a synclinal structure 
in this locality, is based on my own field observations, as is also the faulting in the Muree Beds 
shown on Wallis Creek to the east of Cessnock. Both these modifications were checked in the 
field by Mr. Millard. A full geological description of the area in great detail is contained in 
Professor David’s work already cited. t and a further very useful account of the geology of the 
area, with a note bv Professor C. A. Sussmilch, is given by Professor David in the Guide Book 
to the Excursion to the Hunter River District issued in connexion with the Pan-Pacific Science 
Congress held in Sydney, 19234 
The map shows the Lochinvar Dome to be a distorted and broken structure, the centre 
of which is occupied by the Lower Marine Series, surrounded by the somewhat irregular outcrops 
of the Lower or Greta Coal Measures and the Upper Marine Series, while the Middle and Upper 
Coal Measures lie in the synclinal depressions to east and west. To the south and south-west 
the Triassic rocks, with bold escarpments, formed by the Hawkesbury sandstones, come close to 
the margin of the folding, and lie with marked unconformity on the Upper Marine Series at the 
head of Coongewai Creek. To the north the structure is open, and rocks of Carboniferous age 
outcrop from beneath the Lower Marine Series. 
About the centre of the Dome, south of Lochinvar, is a large mass of hypersthene andesite 
forming the hill of Blair Duguid. Professor David considers this to be the stump of an old volcano 
which was contemporaneous with the Lower Marine Series, and that the andesitic agglomerates 
in the Lower Marine Series, which form a conspicuous feature about 2 miles to the north, are eruptive 
products formed by this old volcano. In the south-east corner is another rather complex mass 
of volcanic lavas and tuffs forming the hill of Mt. Bright, which Professor David considers to be 
chieflv of Carboniferous age with the Lower Marine Series resting unconformably against its margins. 
This volcanic mass is much faulted, a nd is considered to be a “ Horst..” a resistant mass left standing 
by the fracturing and movements which have gone on in the surrounding deposits. § 1 am inclined 
to think that these two volcanic masses have played an important part i n the formation of the 
structure of the Lochinvar Dome. 
Faulting is much more prevalent in the area than is shown in the somewhat diagrammatic 
map which accompanies this Report. The faults are chiefly grouped in north and south and 
south-east to north-west directions. The north and south lines are practically parallel to the 
main axis followed by the fold in its northern part, and which it would apparently continue to 
follow in the southern portion but for later influences which have considerably distorted it in 
this direction. These fractures are older than those which occur on south-east and north-west 
lines, and are shown by Professor David to be displaced by the latter when these newer faults 
cut across them, and this would be expected from the nature of the structure. The north and 
south fault which runs along the western margin of the Dome is known as the Elderslee Fault. 
It has a down-throw to the west which increases from 1,100 feet to perhaps 5,000 feet as we proceed 
from south to north. The large fault which cut across the Dome from south-west to north-west 
south of Greta and Branxton is called the Greta Fault, and has a maximum down -throw to the 
north-east of 1.100 feet. 
The re-entrant angle bounded north, south, and east by the outcrops of the Greta Coal 
Measures around Branxton is a down- faulted block which is synclinal in character. This is 
shown by the well-marked syncline in the Muree Beds which outcrop in this area to the west of 
Branxton. It is curious how this feature is paralleled by the outcropping beds right across the 
Dome on this line, i.e., approximately on the line followed by the Greta Fault. The Kavensfield 
sandstone follows this curve ou both sides of the Dome, so does the outcrop of the. Lower or Greta 
* A little faulting is observable in a railway cutting east of llelford which exposes the crest of this anticline. One fault is a small over.hrust from tin-. 
'■ Mem. of the Geol. Sui v. of N.S.W. — Geol. No. 4, 1907. 
♦ August, 1923 , pp. 10 33. Sec also H. C. Millard on “The Lochinvar Dome." Industrial Australian and Mining Slumlord, Melbourne. 31st July i< -'i 
Thu article contains a we II -reasoned discussion of oil and gas prospects in this area. 
§ Mem. of the Geol. Surv. of A. SAY,- Geology No. 4, 1907, pp. 122 124. 
C. 10071. — 2 
