FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 5)

Reminder that all the maps, diagrams etc referred to in the text have been lost.
CHAPTER 2 CONTINUED
Excursion 2b 
Gerringong- Berry (17 miles) 
This excursion deals mainly with the stratigraphy of the Berry Formation and the effects of differing lithology on landforms and soil fertility. 
Route: Prince’s Highway from Gerringong to Berry, with diversions to Toolijooa and Foxground. 
Gerringong is close to the former centre of Permian volcanic activity. On this excursion, the flows are seen to become thinner and finally vanish while the tuffaceous sediments merge to become one unit, the Broughton Sandstone. 
Stop 1. In the road cutting opposite Gerringong station, the Kiama Sandstone is well exposed. It is much the same as the outcrops seen at Kiama and Bombo, but with a higher proportion of pebbles. 
Proceed towards Berry. Outcrops of Kiama Sandstone are seen for the next two miles, at which point turn left and go to Toolijooa station. 
Stop 2. The Blow Hole Flow is exposed in the railway cutting. The rock is similar to that seen elsewhere and associated with it are masses of agglomerate. This contains black and white calcite, which displays a yellow fluorescence under the influence of ultraviolet rays. 
Return to the highway and continue towards Berry. The road ascends Foxground Hill, where the Bumbo Flow is seen towards the top. Stop just beyond the hill, where the Foxground road branches to the right (1 ½ miles from the Toolijooa corner). 
Stop 3. This small quarry exposes a coarse tuff, part of the Kiama Sandstone. On the slope above are many boulders of latite. The mountain rising beyond this is Curry’s Hill, which is topped by an outlier of the Cambewarra Flow and the Coal Measures. 
From here, the road into Foxground extends about 2 ½ miles. The scenery is very fine and the geology comparatively simple. The valley occupies a syncline in which the Kiama Sandstone is exposed at the southern end and the Bumbo Flow at the northern. 
Broughton Creek, which drains the valley, carries a little alluvial gold in addition to the quartz minerals common in this area. 
Proceed towards Berry. Broughton Creek carries a variety of rock types, similar to those seen at Foxground. Various road cuttings towards Berry expose weathered tuff and the Bumbo Flow, which becomes thin and patchy in this direction. The soil also deteriorates as the tuffaceous nature of the Broughton Sandstone becomes less dominant. A quarry on the left, 3 ½ miles from Broughton Creek, exposes siltstone of the Berry Formation. 
Stop 4. The siltstone is quite weathered and contains little of interest other than a few poorly preserved fossils. It is fairly typical of much of the Berry Formation. 
Continue towards Berry. Stop at a roadside rest area on the right ½ mile further on. 
Stop 5. A normal fault cuts the siltstone in the road cutting. Its displacement seems to be about 20 feet, south side up. The view to the west shows the Cambewarra Range with Berry Mountain standing out.  
Excursion 2c  
Kiama-Robertson-Fitzroy Falls (52 miles) 
The stratigraphy of the Permian and Triassic sequence is seen most completely on this excursion. Younger volcanic rocks of Tertiary age are also prominent and there are good examples of erosion by waterfalls. 
Route: Kiama-Saddleback Mountain–Jamberoo–Minnamurra Falls–Jamberoo Pass–Barren Grounds-Carrington Falls-Robertson-Belmore Falls-Fitzroy Falls 
From the harbour at Kiama, go south along the highway for ½ mile before turning right into Barney Street. Outcrops of pink Kiama Sandstone and a disused quarry in the Bumbo Flow are soon seen on the left and may be examined. Outcrops of the Bumbo Flow occur sporadically for the next 3 miles as the road ascends. After this the Jamberoo Sandstone becomes evident and the Saddleback Flow just before the final steep ascent. 
Saddleback Mtn from Gerringong March 1963
The road then climbs steeply for 350 feet. Sediments of the Illawarra Coal Measures are seen at first, followed by the Bong Bong Basalt, which displays prominent columnar joints. This section is best examined by walking back from the summit. 
The view from Saddleback Mountain August 1966
  

Stop 1.  
Saddleback Mountain (elevation 1750 feet) is an intrusion of  supposedly Ter-tiary age and probably represents the core of an extinct volcano. At the summit, volcanic agglomerate may be seen, surrounded by the basalt already seen in the road cutting. 
There are excellent views in all directions. In the west, Bong Bong Mountain forms the end of the Barren Grounds, capped by Hawkesbury Sandstone. The northern view is often marred by smoke from the Port Kembla industrial complex, but on a clear day the coast is visible from Kiama to Cronulla. Immediately below the mountain lies Werri Beach. The southern view is the most interesting in terms of the area covered by this book. The valley below is Foxground, through which Broughton Creek winds to the Shoalhaven River beyond. Along the coast may be seen in order: Seven Mile Beach, Coolangatta Mountain, Shoalhaven Heads, Crookhaven Heads, Lake Wollumboola, Culburra, Jervis Bay and the Beecroft Peninsula. Beyond this, landmarks are less distinct, but the prominent mountains on the horizon are, from the east, Durras, Boyne, Little Forest, Pigeon House, Talaterang and Tianjara. In the middle distance lies Nowra Hill and a vast expanse of bush beyond. 
Return towards Kiama, turning left for Jamberoo at the bottom of the first steep hill. The road descends through the Cambewarra and Saddleback flows at first, then through the Jamberoo Sandstone and Bumbo Flow, as seen in the ascent on the Kiama side. Turn left at the Jamberoo road, pass through Jamberoo and proceed to Minnamurra Falls. 
Stop 2. The rain forest here contains many unusual species not normally seen this far south and is worth visiting for this reason alone. Information concerning the flora and fauna may be obtained at the reserve.
Upper Minnamurra Falls January 1953
From the Hawkesbury Sandstone cliffs down, the rock types here are the Narrabeen Group, Illawarra Coal Measures, Minumurra Flow, Cambewarra Flow and the Jamberoo Sandstone. The sandstone, which is fossiliferous, outcrops in the creek bed behind the kiosk.  Upstream, the lower falls have formed by the weathering out of a dyke which intrudes the Cambewarra Flow. The upper falls have formed where a sill of nepheline syenite has intruded the Coal Measures, the sill being more resistant than the sediments.  
An interesting variety of rock types may be found in the creek. Coal is fairly common, and the igneous rocks contain colourful zeolite minerals. 
Return on the Jamberoo road and turn right towards Robertson (Jamberoo Pass). At the foot of the mountain, outcrops of the Kiama Sandstone may be seen. The ascent of 1,600 feet reveals few good outcrops, but weathered coal seams are visible towards the top and may be examined. 
Turn left to the Barren Grounds Faunal Reserve just beyond a small creek 3 miles from the bottom of the mountain. 
Stop 3. The Reserve, which has an area of 4,390 acres, was first gazetted in 1956 and is part of a vital system of reserves aiming to retain all types of habitats and the varied life found in them. It is largely composed of heath and swampy land, bounded by cliffs of sandstone with rain forest on the slopes below. 
At the Visitor Centre, a map of the area indicates points of interest. No-one should miss the fine views of the coastal plain from Illawarra Lookout. The Griffith Trail leads to Wonga Falls, at the head of Broger’s Creek, and from here a track leads to the Drawing Room (4 miles) and down to Woodhill Gap (see Excursion 4a). 
From Wonga Falls the trail crosses the heart of the reserve, reaching its highest point at Barren Grounds trig. station (2,182 feet). The left branch leads back to the Visitor Centre while the right, following Surveyor Hoddle’s 1830 route, leads to Bong Bong Mountain and eventually to Saddleback.  
Return to the Robertson road. Red shales of the Narrabeen Group may be examined on the right about 300 yards further on. These sediments, of Triassic age, are widely distributed through the Sydney Basin and are thought to represent volcanic debris redeposited by running water. Some plant fossils may be found here. One mile further on the Hawkesbury Sandstone may be examined. A short climb to the cliff edge will be rewarded by a fine view of the coast. Knight’s Hill, with its TV masts, is an outlier of the Wianamatta Group, mainly shale, overlain by Tertiary basalt. 
Turn left to Carrington Falls, 500 yards past the Kangaroo River.  
Stop 4. These falls mark the limit to which the Kangaroo River has 
Gorge at Carrington Falls March 1973
removed the Hawkesbury Sandstone. The valley is very narrow at this point, a reminder that the width of a valley is often a measure of its age, rather than the erosive capacity of its major stream. 
Potholes and pools in the sandstone bed of the river have yielded small sapphires, zircons and occasionally diamonds. Their origin is obscure, but is probably related to similar deposits near the head of the Nepean River, about 12 miles away, and the Wingecarribee River near Berrima. They are perhaps relics of a former river system which flowed to the sea across this country before it was uplifted. 
Return to the main road. Pass through Robertson and turn left onto the Belmore Falls road. Most of the higher country is underlain by basalt and the rich soil derived from it is responsible for the high productivity of the area. The basalt has protected shales of the Wianamatta Group from erosion, as at Knight’s Hill, but outcrops are usually poor. Good plant fossils have been 
Belmore Falls February 1967
found in some. 
Turn left to Hindmarsh’s Lookout, 5 miles from Robertson. 
Stop 5. Belmore Falls represents the head of erosion of Barrengarry Creek.  The valley below is deeper than that at Carrington Falls, there being outcrops of the Narrabeen Group, Coal Measures and Berry Formation immediately below the falls. 
Proceed to Fitzroy Falls. 
Stop 6. In Fitzroy Falls, Yarrunga Creek has produced the highest fall in the district.  The erosion, as at Belmore and Carrington, is 
Hawkesbury Sandstone at Fitzroy Falls November 1967
headward. Paths lead to lookouts on both sides of the gorge and the descent to the bottom shows interesting outcrops of Coal Measure sediments. The view down the valley is partly blocked by an outlier of sandstone (Mt. Carrioloo).  
Mt. Scanzi may be seen to the left of it in distance. See Excursion 4d, Stop 3. 
Fitzroy Falls April 1960
Questions  
1. Discuss the coastal topography formed from different members of the Berry Formation. 2. Why was Kiama developed on its particular site? 3. Give an account of the different types of igneous rocks to be seen in the Kiama district. 4. What part has the Hawkesbury Sandstone played in the development of the landscape? 5. What evidence suggests that the Blow Hole Flow was of submarine origin? 6. Discuss the influence of dykes on the development of particular landforms. 
  

Unconformity near Robertson March 1973
Basalt on Wianamatta Group shales


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