FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 14)

Chapter 8. The Tomerong District 
In earlier days, when there were few casual visitors to the South Coast, Tomerong was much more a rural centre than it is today. The growth of holiday areas around Jervis Bay and St George’s Basin has rendered it less important. 
Tomerong is situated where the southern road first passes through the Nowra Sandstone onto the widespread Wandrawandian Siltstone. The change is marked by a noticeable improvement in the soil, and this in turn has led to the growth of spotted gums and turpentine, in contrast to the poorer types growing on sandstone soils. The sawmills around Tomerong and Wandandian capitalise on this forest wealth and provide local employment. 
North and west of Tomerong are outcrops of the overlying sandstone and the Berry Formation. Elsewhere, the Wandrawandian Siltstone is the dominant rock type, except along the shores of Jervis Bay, where a dome structure has brought the Conjola Formation to the surface. The same structures seen west of Nowra have folded the strata south to the ocean at Wreck Bay; in addition the Parma Monocline has acted as a line of uplift west of Tomerong. 
Excursion 8a 
Upper Parma Creek (18 miles return) 
Interesting erosional features and the effect of minor folding are the main things seen on this excursion. 
Route: Tomerong-Blackbutt Range-Hell Hole-Parma Creek Falls-Turpentine Road-Tomerong 
Take the highway north from Tomerong. Immediately north of the town, there are road cuttings where the Wandrawandian Siltstone and a large dyke are exposed. 
Stop 1. The dyke, about 60 feet wide, is composed of olivine dolerite and shows up in the cutting because of its different weathering characteristics. The strata it intrudes are typically bowed up by the dyke, a feature visible near all of these large intrusions. This particular dyke may be traced for several miles, seldom varying from its straight path. 
The road ascends into the Nowra Sandstone, here much siltier and thinner than at Nowra. Cuttings exposing the Berry Formation are seen near the top of the climb, and these contain typical marine fossils. 
Stop where a poorly defined track leaves on the left, 0.6 miles past the dyke. 
Stop 2. The lower part of the Nowra Sandstone is exposed in an old quarry, ¼ mile along this track. The siltstone in the quarry and down the gully abounds in fossils. The majority are preserved in calcite and some excellent specimens may be obtained here. 
Return to the highway and continue another mile towards Nowra. Turn left along the Blackbutt Range fire road. After 2 miles through typical spotted gum forest, the road begins to rise where the Parma Monocline has elevated the strata. Turn right along Parma Creek Road. Timber tracks off to the left, now largely overgrown, lead out to the Hell Hole, ½ mile west of the road. 
Stop 3. Hell Hole is a bottleneck canyon, similar to the Grose Valley in the Blue Mountains. It is bounded by cliffs of sandstone, about 40 feet high, and the dip of the strata has caused Parma Creek to carve its valley in the unusual form shown on the map. 
Continue to where the road leaves the Berry Formation and crosses the sandstone bed of Parma Creek. 
Parma Creek waterfall; July 1967
Stop 4. There are many interesting things to be seen by walking downstream for ½ mile, The Nowra Sandstone is divided by a siltstone bed, as it is at Falls Creek. Both the upper and lower sandstones have been responsible for waterfalls, by whose retreat a mile long gorge has been created. Below the second fall, a sizeable tributary joins Parma Creek and it too has waterfalls where these beds outcrop.  
Parma Creek pothole July 1967
The Wandrawandian Siltstone outcrops below the falls and contains many fossil brachiopods. Other fossils are to be found in loose blocks of rock in the creek bed. 
There are numerous potholes in the creek and one of these is large enough to swallow most of the stream when the water is low. In this way the creek constantly lowers its bed.  
Return to the Blackbutt Range fire road and turn right. After two miles, this leads to the Turpentine Road, 5 miles from Tomerong. There are two steep descents along the Turpentine Road and these are the only places where the Nowra Sandstone is seen. The first of these is due to the Parma Monocline and at the second, the road descends to the Wandrawandian Siltstone in a similar fashion to the descent on the highway north of Tomerong. 
Excursion 8b 
Jervis Bay and St George’s Basin 
This excursion takes in a long stretch of coastline, from Huskisson to Sussex Inlet. The underlying rocks belong to the Wandrawandian Siltstone and the Conjola Formation. 
Route: Most places of interest are along the coast and will be considered southwards in order from Huskisson. There is little variety in the geology other than a few dykes on the Wreck Bay shore. 
Huskisson. The Wandrawandian Siltstone is exposed for ½ mile along the shore from Currumbene Creek to Tapalla Point. It has a north easterly dip and is most notable for the numerous glendonites it contains. These are accompanied by marine fossils and erratics of schist, quartzite and granite. In 1886, a bore was put down at Huskisson in search of coal, poor seams of which were struck at a depth of 840 feet. The discovery of coal in the Clyde River gorge had created considerable interest and it was hoped that Jervis Bay might be developed as a port, but the plans came to nothing following an unfavourable government report in 1890. The coal seams were studied in every available outcrop and by the sinking of a new bore west of Tomerong. This bore penetrated coal seams of no commercial value and no further action has been taken towards coal mining near Jervis Bay. 
Vincentia. Sandstone of the Conjola Formation outcrops from Vincentia southwards, with the exception of a small outlier of siltstone at Lamb’s Point. The north easterly dip increases towards Hyam’s Beach, reaching 15° or more. This is the result of folding parallel to the Parma Monocline; in this case the dominant structure is the Bhewherre Anticline, also seen just west of Nowra. 
Commonwealth Territory. The southern headland of Jervis Bay, like the northern, is composed of sandstone blanketed by extensive deposits of wind blown sand. Sandstone cliffs exceeding 400 feet in height front the Tasman Sea and present an unforgettable sight to the mariner. In 1770 Cook noted these cliffs and named Cape St George because of the date of its discovery (24th April). Cook reported the entrance to Jervis Bay but thought it not worth the trouble to go out of his way to enter it. So, because Cook was too far out to sea, Jervis Bay was passed up in favour of Botany Bay and the course of Australian history altered. Had the ‘Endeavour’ anchored here, then Sydney might have been founded where the RAN College stands today. 
The places referred to below may be located by their corresponding letters on the map. 
Green Patch (A) is a popular picnic spot. Nearby was the now vanished settlement of New Bristol, one of many attempts to develop this impressive bay as a major port. 
Hole in the Wall (B) is an example of the combined effect of wind scour and salt laden spray. A natural sandstone wall has been effectively perforated by the process. 
Bowen Island (C) is separated from the mainland by a narrow and dangerously shallow channel. 
Stoney Creek (D) is a well known fishing spot where access may be had to the extensive rock platforms near Cape St George.  
At Steamer’s Beach (E) the cliffs are the highest in the district and the sandstone exceeds 450 feet in thickness. Sand hills spill right down the steep slope into the sea at this beach. 
Boat Harbour or Whiting Beach (F) has formed by the erosion of a dolerite intrusion. It resembles the Tomerong dyke in the way it has arched the sandstone, but in this case there has been considerable contact metamorphism and the adjoining sandstone has become hard quartzite. Minor black sand deposits occur on this beach, containing ilmenite, zircon and rutile. 
Summer Cloud Bay (G) takes its name from a barque wrecked here in 1870. A weathered out dyke may be seen in the cliff face. 
Cave Beach (H) is so named because of a weathered out dyke on the southern headland. This dyke has eroded into a tunnel of larger than usual dimensions.  
The Clay Pits (J) have yielded quarts crystals similar to those found near Currarong (see Chapter 7). 
Lakes McKenzie and Windermere (K) are the result of streams being dammed by shifting sand hills. 
St George’s Basin (M) This body of water lies along the same syncline as that seen at Cabbage Tree Creek, on the Yalwal road. Its origin seems to be the same as the other coastal lagoons in the area. The lower valleys of Wandandian and Tomerong Creeks have been drowned and the bay formed has been blocked by sand hills. Only Sussex Inlet now provides access to the sea. 
Sporadic outcrops of the Wandrawandian Siltstone occur along the northern shore of the Basin and occasionally fossils may be found in these. 
Questions 
1. Show how folding has led to the disposition of rock types seen in upper Parma Creek. 2. Compare the Nowra Sandstone outcrops near Tomerong with those seen at Nowra. What is the main difference? 3. Give evidence for the existence of a series of parallel folds extending through Jervis Bay, the Commonwealth Territory and St George’s Basin. 4. Discuss the effect of sand hills in modifying an existing topography. 5. Suggest reasons why a major port has not developed at Jervis Bay. 6. Compare the landscape characteristically produced from each member of the Shoalhaven Group in the Tomerong district. 
Song Studies. Bible studies based on hymns and songs
Shoalhaven District Geology.

Year 11 Nowra High School Geology Field Trip June 1967

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