FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 21)

Chapter 13. The Termeil and Durras Districts 

Until tourism brought the present growth of holiday resorts, this part of the coast remained relatively unknown. Much of it is still unspoiled and every effort should be made to keep it that way. This is especially true of the coastline between Pebbly Beach and Pretty Beach, where the slopes of the Murramarang Range fall steeply to the sea and tiny islets lie inshore. The whole of the country from Bawley Point south to Bateman’s Bay is thickly covered by spotted gum forest and has been reserved as a State Forest. The only use of the land for farming has been near Termeil, Murramarang and Durras Mountain; the rest is virgin bush. 

The Conjola Formation dominates the geology and considerable progress has been made recently towards the unravelling of its stratigraphy. There is a greater thickness of sedimentary rock here than has been measured over most of the area north of Ulladulla and it has been subdivided into several members. 

Associated with the Permian sediments are a number of isolated flow remnants, resembling those of the Gerringong Volcanics further north. It is possible that there was volcanic activity here early in the history of the Sydney Basin as well as in the Hunter Valley. 

The Termeil Essexite intrusion extends for 5 miles along the coast from Bawley Point and it appears to have formed about the same time as the Milton Monzonite intrusion. It is also possible that it is related to the flow remnants mentioned above. 

The basement rock is most often the same Ordovician slate seen in many places in the Shoalhaven district. Underlying the Permian near Durras Lake is another group of metamorphic rocks, the Wagonga Beds. They are composed of highly folded dark slate and quartzite of supposed Cambrian age. Their outcrop extends north from the Narooma district, where they form spectacular coastal exposures. 

Excursion 13a 

Termeil- Murramarang (40 miles) 

The Termeil Essexite and the Durras Flow are the principal features of this excursion, which also includes large areas of the Conjola Formation. 

Route: Burrill Lake-Tabourie Lake-Termeil-Bawley Point-Murramarang-Kioloa-Merry Beach-Durras Mountain-Termeil 

From Burrill Lake, the highway runs south past extensive pine forests to the small inlet of Tabourie (or Toubouree) Lake. The plantations were considerably damaged by fire several years ago and many of the trees did not recover. Turn left just before the lake and stop at Toubouree Point. 

Stop 1. Crampton Island is composed of sandstone and conglomerate dipping gently to the east. It is frequently linked to the shore by a sand spit or tombolo. Wairo Beach separates Lake Tabourie from the sea in much the same way as Bhewherre Beach cuts off St George’s Basin. The coast south to Bawley Point is as yet unspoiled by encroaching ‘development’ and it is to be hoped that at least some of it can be preserved in its present state. 

Continue south along the highway. Turn left at Termeil and proceed to Bawley Point.  

Stop 2. The little beach at Bawley Point has outcrops of Conjola sandstone at its northern end and essexite at its southern. Unfortunately, no contact between the two can be seen, either here or anywhere else along the coast. By inference, the essexite is assumed to be an intrusion. 

The headland south of the beach is bordered by superb outcrops of essexite. It is quite coarse, being visibly composed of black pyroxene and pale labradorite. Olivine and nepheline are less common. It more closely resembles gabbro than any other common rock. On weathered surfaces, the rock shows an unusual mottled appearance. 

From Bawley Point, a road parallels the coast for several miles. Turn left at Rosemary Avenue, 1 mile south, and then veer right until the road reaches Murramarang Beach. 

Stop 3. This is a place of exceptional interest. The essexite exposures here are similar to those at Bawley Point. Black sand has accumulated at the extreme northern end of the beach where a small creek runs into the sea. The heavy minerals in it are probably derived from the nearby intrusion and are more concentrated here than elsewhere. 

Many years ago, an attempt was made to mine gold from the sand on this beach. Recent applications to mine have been rejected. The black sand is mainly magnetite and ilmenite and is noticeably darker than the rutile bearing sands of the north coast of NSW. It is possible to wash very fine gold containing a little platinum using a prospector’s dish. 

Just beyond the small creek is one of the largest aboriginal middens in NSW. Acres of sand hills are strewn with shell fragments, charcoal, and rock chippings. The visitor should take care not to despoil this site especially since it has not been thoroughly studied by archaeologists. 

Brush Island lies just off the southern end of the beach. It is the largest of the numerous small islands along this part of the coast and is a prominent landmark from places like Warden Head and Durras Mountain. The waters around the island are very popular with spear fishermen. 

Continue south towards Kioloa. The old homestead on the right is ‘Murramarang’ from which the locality takes its name. The range of hills behind contains scattered outcrops of a basaltic lava flow, the Murramarang Flow. The entire coastal fringe, where not sand covered, is composed of essexite, outcrops of which may be seen at Kioloa, O’Hara Head, and Merry Beach. 

Turn left at Merry Beach. The small hill to the left of the road is composed of essexite.  

Stop 4. Essexite forms the outcrops at the northern end of Merry Beach and Conjola sandstones the southern end. The Conjola Formation contains fine and coarse conglomerate in this vicinity and their pebbles have produced some outstanding pebble beaches (see Excursion 13b). 

Near the Pretty Beach turnoff the road leaves the coast and winds through spotted gum forests towards the Prince’s Highway. After 3 miles, keep to the left where the road turns right at a forestry hut. 

By following these forestry roads, the summit of Durras Mountain is eventually reached, 5 miles from Pretty Beach. 

Stop 5. The Durras Flow occupies the highest part of the range, for a distance of about a mile. The rock is a type of porphyritic andesite, resembling the latites of Kiama. As the summit is private property, the landowner’s consent should be sought before entering. 

Durras Mountain has an altitude of 930 feet, and affords unsurpassed views in all directions. The sea and a beautiful stretch of coastline lie close below to the east. The northern view takes in the coast as far as Kiama, where Saddleback Mountain may be seen. In the south, Durras Lake, Bateman’s Bay, and Mt Dromedary are prominent. In the west is the Pigeon House and nearby sandstone mountains, as well as the Budawang Range extending southwards through Currockbilly and Clyde Mountain towards Araluen. 

Return to the Merry Beach road and continue towards the highway. The sandstone eventually gives way to the Ordovician basement and this continues along the highway towards Termeil. Three miles south of Termeil, and a similar distance north along the highway, the Conjola Formation may be again be seen outcropping. 

Excursion 13b 

North Durras and Pebbly Beach (18 miles) 

The Conjola Formation along this part of the coast contains many examples of sedimentary structures, which are better seen here than elsewhere in the Shoalhaven district. 

Route: East Lynne-North Durras-Depot Beach-Pebbly Beach-Prince’s Highway 

Leave the highway at East Lynne, 10 miles south of Termeil. The road passes over poorly exposed slate for 1 ½ miles and then over the Conjola Formation. Keep to the right 3 miles from the highway. One mile further on, the road passes through Lovell’s Pass, where poorly fossiliferous sandstone and siltstone is exposed. Shortly after, the road divides. The left branch leads to Depot Beach. Take the right branch, which leads to North Durras. 

Stop 1. Durras Lake is another of the coastal lagoons which resulted from the postglacial rise in sea level. Point Upright, so named by Cook in April 1770, is a landmark to the north and may be approached via the beach. From the entrance to the lake to Depot Beach is a walk of 2 miles. Many of the features of interest may be approached from the Depot Beach end with less effort. 

The strata here belong to the lowest part of the Conjola Formation, which has been correlated with the Dalwood Group (Lower Marine) of the Hunter Valley. The sediments are mainly siltstone and shale with prominent interbedded conglomerate. The conglomerates contain the typical angular blocks common in the Shoalhaven Group. The finer sediments display many interesting features which illustrate their origin. Wash outs, ripple marks, and worm tracks suggest shallow water sedimentation. Such features have rarely been observed elsewhere in the Shoalhaven district. 

Proceed to Depot Beach. 

Stop 2. A good view of Grasshopper Island may be had from Depot Beach. There are several small sandstone islets along this part of the coast, though there seems to be no good reason for their concentration here. The rock platform at the southern end of the beach may be followed around to Point Upright (Stop 1). Similar sediments are exposed north of the beach but are less accessible. 

Return along the road towards the highway. Turn right after 2 ½ miles and again 1.4 miles further on. From here the road descends sharply to Pebbly Beach. 

Stop 3. Sediments of the Conjola Formation outcrop here also. There is little of interest in the siltstones at the northern end of the beach. Conglomerates outcrop near the southern end and these have given rise to extensive pebbly beaches south of the camping ground. These pebbles, being derived from the neighbouring conglomerates, are largely composed of the rock types found in them – quartz, quartzite, chert, various types of hornfels, rhyolite, and other resistant rocks. Agate and chalcedony are occasionally found and these, along with other attractive pebbles, are often collected for lapidary work. 

Fossilised logs, some of them preserved as coal, may be seen in the cliffs and on the rock platform. These apparently floated from the nearby shore, since these sediments are definitely of marine origin. 

Return to the highway by ascending the hill and turning right (5 miles). 

Excursion 13c 

North Head and South Durras (27 miles return) 

The southernmost Sydney Basin sediments and their associated unconformities are features of exceptional interest seen on this excursion. 

Route: Bateman’s Bay-Benandrah-South Durras-North Head-Flat Rock-Dark Beach-South Durras-Benandrah-Bateman’s Bay 

Proceed north along the Prince’s Highway from the Clyde River bridge at Bateman’s Bay. Road cuttings expose lower Palaeozoic slate and phyllite. Turn right along Berrima Parade, 1 mile north of the river. This leads to New Haven Surfside Beach on Bateman’s Bay. 

Stop 1. Outcrops of highly folded and faulted siltstone occur on the shore and an aboriginal midden is located behind the beach. 

Return to the highway and continue northwards. Two miles further on, a road branches right to Long Beach, where folded strata may be examined. Turn right at Benandrah, 5 miles from Bateman’s Bay, along the South Durras road and turn right off this onto the North Head fire road 1 mile from the highway. This leads, after 5 miles, to a point above the sea where fine views are to be had both up and down the coast. 

Stop 2. Rounded gravel occurs here about 100 feet above sea level. This may represent a raised beach, evidence of a former higher sea level, or it may be the remnants of an outlier of Permian conglomerate. 

A track leads down to the sea where hard black slate forms rugged outcrops and present an entirely different appearance to the familiar Permian exposures. Pebble beaches have formed from these hard rocks and similar pebbles are abundant in nearby Permian outcrops, indicating that these rocks were exposed to erosion even then. 

Take the Coast Road northwards. Three miles from North Head, a branch leads out to a grassy point where the most southerly exposure of Sydney Basin sediments may be examined. 

Breccia bed in the lowermost Permian at Flat Rock November 1967

Stop 3. From this locality, known as Flat Rock because of a number of small sandstone stacks off the point, an extensive view extends south to Mt Dromedary and north to Brush Island. The strata dip noticeably to the north, but their base is not visible. However, basement rocks are exposed south of the little beach. 

The sediments are quite coarse and are frequently composed of blocky breccia beds, with boulders up to 3 feet across. These are of hard slate and quartzite, identical to the adjoining outcrops. 

Continue towards South Durras. Another side track leads into Dark Beach, about 1 mile north of Flat Rock. 

Stop 4. A classic unconformity is exposed along the southern edge of this tiny beach. The Permian strata rest on an uneven surface composed of nearly vertical Wagonga beds. Elsewhere around the inlet, extensive breccia beds merge into sandstone above

Base of the Permian resting on the Wagonga Beds at Dark Beach November 1967 

(belonging to the Conjola Formation) and slate below, without any clear cut boundary. The invasion by the sea in Permian time evidently bared some areas of accumulated debris and deposited this in nearby depressions. 

South Durras is only a short distance north of this point, about 1 mile by road. 

Stop 5. The Conjola sediments exposed in the rock platform at South Durras resemble those at Point Upright, 2 miles to the north. The same sedimentary structures and fossils may be found, but much of the pebbly sandstone is littered with slate fragments, indicating that outcrops of basement were close. 

Wasp Island, composed of similar sandstone, lies just offshore and is well seen by walking from the southern end of the south beach towards Dark Beach. 

The return trip to Bateman’s Bay via Benandrah includes a further example of an unconformity, 1 mile from South Durras, but this is much less convincing than that seen at Dark Beach. 

Questions 

1. Discuss the evidence in favour of Permian volcanic activity in the Termeil district. 

2. Compare the sediments seen at Flat Rock, Point Upright and Crampton Island. 

3. What do the sedimentary structures observed at Point Upright and South Durras tell us about the depositional environment which prevailed then? 

4. The present edge of the Permian sediments tends to rise away from the present coastline. Why is this so? 

5. Suggest reasons why islands are more common between Bateman’s Bay and Ulladulla than elsewhere south of Sydney.