FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 17)

Chapter 9 continued 
Year 7 class Moss Vale High School  at 
Bungonia Caves November 1973
Excursion 9c

Bungonia, South Marulan and Tallong
These are just a few of the places of interest across the river, which are worth a visit as part of excursions to the Goulburn district.
Bungonia Caves
An extensive area of Silurian limestone crops out from South Marulan over a distance of 7 miles in a south westerly direction. The caves are reached by travelling east from Bungonia village. Part of the area is in a reserve and was formerly maintained for tourists until visitor numbers dropped as people preferred to visit the more spectacular caves elsewhere in NSW.
The Lookdown is the best known feature here. There is a very
The Lookdown December 1963
sharp drop of 1,200 feet to Bungonia Creek. This may be descended with care to the right of the lookout. The limestone here contains typical Silurian fossils, particularly the coral Favosites. Grykes or solution grooves are also prominent.
The Slot Bungonia Gorge from 
Adam's Lookout December 1963
Adam’s Lookout is even more spectacular, especially if Bungonia Creek is in flood. The creek runs through a very narrow gorge known as The Slot. With care, the descent to the creek may be made, but scree slopes should be avoided.
There are numerous caves, many of which open up from the bottom of depressions or sink holes.
These are identified by a number at their entrance and should not be entered except by experienced speleologists with proper equipment. There have been a number of fatalities here in recent years, caused by inexperience or fatigue.
In the Fossil Cave December 1974
Fossil Cave (B4) contains water worn passages exposing fossils in the limestone. It connects with B5.
Hogan’s Hole (B5) contains several long drops.
The author in the Grill Cave December 1968
Bungonia Cave (Grill Cave) (B9) was formerly a tourist cave and is now badly defaced. There are still some attractive parts in its more remote corners. Ladders and wire netting from the tourist days remain in place. Foul air can be a problem in the lower levels.
Drum Cave (B13) has a drop of 140 feet just beyond the entrance. The passages below contain interesting formations but are better known for their bat colonies and foul air.
In Holland's Hole December 1974
The Efflux (B67). This is a stream cave where water escapes from the plateau above. Patient excavation over a long period has still not allowed access to the extensive passages believed to exist upstream.
The author in Argyle Hole June 1975

South Marulan
From Marulan, a road leads out, over granodiorite of the Marulan batholith, to the edge of the Shoalhaven gorge. In the quarries of the Southern Portland Cement Company, the limestone has been
converted to a coarse granular marble. At the northern end of the quarry, just below the offices, several basic
Marulan quarry from Long Point Tallong June 1971
dykes intrude the marble as well as a poorly defined ore body containing pyrite, arsenopyrite and chalcopyrite. Slate is exposed on the eastern side of the quarry. This appears to be separated from the limestone by a major fault.
Dykes cutting the marble at South 
Marulan quarry December 1966

Tallong
At Long Point Lookout, there is a superb view of the Shoalhaven gorge. The track descending to the lookout exposes black slate in which occasional Upper Ordovician graptolites may be found.
The track leading south from the lookout reveals several small outliers of Permian conglomerate resting on the slate.
The Big Bend Shoalhaven River Long Point Tallong June 1960
The Shoalhaven at this point bends sharply to the east. Some geologists believe that the river formerly ran north to join the Wollondilly River and that some time after the uplift, a stream eroding inland from the coast captured this part of the river, along with Budgong Creek, Kangaroo River and Tallowal Creek. Old gravel on the present surface near Tallong has been regarded as evidence for this hypothesis.
From Tallong railway station, Caoura road runs for 15 miles through basalt country, leading eventually to a point above the junction of the Shoalhaven and Kangaroo Rivers. See Excursion 4d, Diversion 2. Opalised wood and agate have been found beneath the basalt and the trip is worthwhile for the extensive views obtained en route.
Questions
1. Discuss the mineralisation of the basement rocks north of Sassafras.
2. Outline in detail an unconformity observed in this area.
3. Account for the present distribution of basalt at Sassafras, Quiera, Tolwong, and Caoura.
4. Present evidence for river capture in the Tolwong district.
5. Give reasons for the sparse population of the Ettrema-Sassafras-Tolwong areas.
6. Suggest reasons for the persistence of the Nowra Sandstone over such a wide area.
7. Discuss the probability of further mineral discoveries in the Ettrema, Touga, and Tolwong districts.


Calcite South Marulan quarry September 1966

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