Shoalhaven District Geology

FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 23) CHAPTER 15: THE CLYDE RIVER VALLEY T aking its rise at an elevation of 2,500 feet near Sassafras, this small river flow south and descends by way of a great canyon to a level of 200 feet at Yadboro. It does this in less than 20 miles, yet it is a further 40 miles to the sea downstream. This is a peculiar result of the dip of the Shoalhaven group sediments. At one time, these must have extended further south than at present. When the area was uplifted, it was tilted to the north, so that the ancestral Clyde River had to erode its bed against this trend.  This undoubtedly led to the formation of many waterfalls and the evolution of the canyon upstream from Yadboro.  The southern edge of the sandstone scarp presents a bold face and is broken into numerous outliers. Some such as The Castle and the Pigeon House are well known to bushwalkers, but there are many others. They all have a similar structure, being capped by cliffs of the...

  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 Ul...

  FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 20) CHAPTER 12.  The Milton-Ulladulla District   The Milton intrusion dominates the geology of this part of the country. Its rich soils lie conveniently close to Ulladulla Harbour and settlers began to arrive here about 1830. However, apart from the country underlain by the Milton Monzonite, the rest of the landscape has changed little since Cook first viewed it in 1770.  Apart from the igneous rocks near Milton, The Conjola Formation is dominant in this area. In recent years there has been a revision in the nomenclature of the Formation and it is now known to consist of sediments of widely varying ages, all within the lower Permian. Contrary to earlier ideas, the lower beds are equivalent to the lower part of the Dalwood Group in the Hunter Valley. Some parts of what has been called the Conjola Formation are as young as the lower Maitland Group. Research into this aspect of Shoalhaven district Geology is still in prog...

  FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 19) Chapter 11   Tianjara and the Little Forest Plateau     Among the landmarks of the Shoalhaven district is the  Tianjara  group of mesas. They lie about 5 miles south of the Braidwood road, near Tianjara Falls. Their flat surfaces, bounded by cliffs and steep slopes make them obvious from all directions, but particularly from the north. They are easily visible from Bundanoon, Saddleback, and Durras Mountain.  Extensive outliers of the Berry Formation cap the coastal hills south from Tianjara Falls to the Little Forest Plateau. This is uninhabited country, used as a military practice area and out of bounds from time to time. The sediments of the Berry Formation are rather coarser than those further north. The presence of the mesas may be due to the peculiar resistance of the strata in this area. Some geographers have suggested that they may be relics of a former land surface, uplifted and lar...

FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT                                              (PART 18) Chapter 10. The Wandandian and Conjola Districts   This is largely an area of uncleared bushland. Features of interest lie along the highway or on the coastal strip. Other than the Wandrawandian Siltstone and the Conjola Formation, the only variation in the geology is provided by an occasional dyke or inlier of basement rocks.  Several dolerite dykes will be seen on these excursions; they are all similar, being composed of a bluish-black olivine dolerite with phenocrysts of plagioclase up to 1 inch across. The dykes are up to 60 feet wide and are traceable for several miles.  The deep valleys of Wandandian and Conjola Creeks have exposed highly folded strata of unknown age, usually taken to be Ordovician like the metamorphic rocks of Tolwong and Nerriga. These have...