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Friday, 19 July 2019

FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 24): REFERENCES MINERALS GLOSSARY

References 
Andrews EC: “Report on the Yalwal Gold Field” (Min.Res.NSW, 9) 1901 
Branagan DF and Packham GH: “Field Geology of NSW” (Science Press) 1967 
Card GW and Jaquet JB: “The Geology of the Cambewarra Mountain, NSW” (Rec.Geol.Surv.NSW, 8, 261) 1903 
Harper LF: “The Geology of the Gerringong District” (Rec.Geol.Surv.NSW, 8(2) 94) 1905 
Harper LF: “Geology and Mineral Resources of the Southern Coalfield” (Geol.Surv.NSW Mem 7) 1915 
Nashar B: “Geology of the Sydney Basin” (Jacaranda) 1967 
Packham GH (Ed): “The Geology of NSW” (J.Geol.Soc.Aust. 16 pt 1) 1969 
Paix JG: The Geology of the Shoalhaven Shire” (Shoalhaven Shire Council) 1968 
Taylor TG: “Sydneyside Scenery” (Angus and Robertson) 1958 
Ulladulla and Wollongong Geological Sheets and Explanatory Notes: (Dep. Mines NSW) 1966   
Year 12 Geology Class at Westley Park September 1984

Glossary: Rock and Mineral Names 
AGGLOMERATE Coarse, angular, pyroclastic rock 
AMETHYST Purplish variety of quartz 
AMPHIBOLES Mineral group, complex aluminosilicates 
ANDESINE Member of the plagioclase family of felspars ANDESITE Volcanic rock composed mainly of andesine and ferromagnesian minerals 
APLITE Fine grained dyke rock often found intruding coarse igneous rocks 
ARKOSE Sedimentary rock rich in felspars; may be derived from weathered granite 
ARSENOPYRITE Mineral, FeAsS, commonly called mispickel or arsenical pyrites 
AUGITE Dark mineral of complex formula, one of the pyroxene group 
BASANITE Volcanic rock resembling basalt, but containing minerals such as nepheline in addition 
BIOTITE Common dark coloured variety of mica 
BORNITE Peacock copper ore, Cu5FeS4, frequently displays an iridescent purple tarnish 
BRECCIA Fragmental rock composed of angular fragments. May be pyroclastic but finer than agglomerate 
CASSITERITE Mineral, SnO2, tin oxide, stream tin CHALCEDONY Waxy variety of quartz composed of microscopic crystals 
CHALCOPYRITE Golden copper ore, CuFeS2 
CHERT Sediment or residue composed largely of minute quartz particles 
CHLORITE Green micaceous mineral, commonly formed during metamorphism or weathering 
DOLERITE Common basic igneous rock of medium crystal size ESSEXITE Igneous rock resembling gabbro, but containing some nepheline 
FELSPAR Large group of aluminosilicate minerals, present in most rocks 
FLUORITE Mineral whose formula is CaF2 
GABBRO Plutonic igneous rock composed mainly of plagioclase, olivine, and pyroxenes 
GALENA Common lead mineral, PbS 
HAEMATITE Common iron ore, Fe2O3 
HORNBLENDE Dark mineral of complex formula, one of the amphibole group 
HORNFELS Fine grained metamorphic rock, the result of the intense heating of a silty sedimentary rock 
ILMENITE Mineral whose formula is FeTiO3 
JASPER Coloured impure of chalcedony 
LABRADORITE One of the plagioclase family of felspars LAMPROPHYRE Intrusive igneous rock rich in phenocrysts of ferromagnesian minerals 
LATERITE Residue of weathering, rich in iron and aluminium oxides 
LATITE Volcanic rock containing approximately equal parts of plagioclase and potassium felspars 
LITHIC SANDSTONE Sandstone composed largely of rock fragments 
MAGNETITE Dark magnetic iron mineral, Fe3O4 
MONZONITE Plutonic rock, similar in composition to latite NEPHELINE Rock forming mineral, (Na,K)Al SiO4 
NORITE Variety of gabbro 
OLIVINE Common family of greenish rock forming minerals, (Fe,Mg)2SiO4 
ONYX Variety of chalcedony composed of coloured, parallel bands ORTHOCLASE Potassium felspar, KAlSi3O8 
PEGMATITE Coarse igneous dyke rock usually found intruding bodies of granite 
PHYLLITE Metamorphic rock, midway between slate and schist PLAGIOCLASE Family of sodium-calcium felspars, ranging from NaAlSi3O8 (albite) to Ca Al2Si2O8 (anorthite) 
PYRITE Common brassy mineral, FeS2 iron pyrites, fool’s gold PYROLUSITE Manganese dioxide, MnO2 
PYROXENES Mineral group, represented by ABSi2O6 where A and B are metals 
QUARTZ FELSPAR PORPHYRY Common intrusive rock, containing phenocrysts of quartz and felspars 
QUARTZITE Metamorphic rock derived from sandstone RHYOLITE Flow banded volcanic rock related to granite in composition 
RUTILE Titanium dioxide, 
TiO2 SCHIST Metamorphic rock in which micaceous minerals are dominant 
SHALE Fine grained, layered sedimentary rock 
SILTSTONE Fine grained sedimentary rock in which layering is not prominent 
SLATE Fine grained metamorphic rock notable for its well developed cleavage 
SPHALERITE Zinc blende, ZnS 
SPOTTED SLATE Slate in which individual crystals are prominent STANNITE Complex ore mineral, Cu2FeSnS4 
SYENITE Plutonic igneous rock, composed essentially of orthoclase and ferromagnesian minerals 
TRACHYTE Volcanic rock related to syenite 
TUFF Fine grained pyroclastic sediment 
ZEOLITES Group of hydrated aluminosilicate minerals 
ZIRCON Zirconium silicate ZrSiO4   
Upturned Strata Shoalhaven River September 1978
Glossary: Descriptive terms 
ACIDIC  As applied to igneous rocks, containing more than 66% SiO2 by analysis  
ADIT Horizontal mine passage from the surface AMGYDALOIDAL Applied to volcanic rocks, meaning contains cavities (amygdales) filled with secondary minerals 
ANTICLINE Fold in which strata are arched upwards BASEMENT Older, more altered rocks lying beneath a sedimentary basin 
BASIC As applied to igneous rocks, containing less than 52% SiO2 by analysis, but more than 45% 
BATHOLITH Large body of intrusive igneous rock, commonly granitic in appearance  
BRACHIOPODS Group of marine invertebrates, having two dissimilar shells (valves), each of which is bilaterally symmetrical CLASTIC DYKE Body of sediment forced by pressure into cracks in the beds above or below 
COLUMNAR JOINTING Pattern of cracks caused by cooling which breaks a body of rock into columns, commonly hexagonal CONCRETION Body of mineral formed around a nucleus within the fabric of a rock 
CORRELATE The determination of the age equivalence of various rock formations 
CRINOIDS Group of marine organisms characterised by a cup, with radiating arms, attached to the sea floor by a stem 
CROSS BEDDING Arrangement of strata at an angle to the horizontal caused by current deposition 
DEUTERIC Term applied to alteration of an igneous rock by solutions after crystallisation has ceased 
DYKE Intrusive body cutting across adjacent rocks 
ERRATIC Applied to transported rock fragments foreign to the area where found 
ESTUARINE Applied to the region where fresh water drainage systems meets the sea 
FACIES As applied to sediments, the nature of the sedimentary material 
FERROMAGNESIAN Containing iron and magnesium FLUORESENCE Emission of visible light by a substance when exposed to ultraviolet rays 
GANGUE The nonmetalliferous components of an ore body GLENDONITE Type of concretion common in Permian sediments which crystallised in near freezing bottom mud 
GRAPTOLITES Extinct group of marine organisms, found in floating colonies 
GROUNDMASS Material between the phenocrysts in a porphyritic rock 
GRYKE Solution groove on a limestone surface 
HYDRATION Combination with water 
IGNEOUS Formed from the molten or partially molten state INLIER 
Body of rock surrounded by younger rocks, produced by erosion INTERMEDIATE As applied to igneous rocks, containing between 52 and 66% SiO2 by analysis 
INTRUSION A body of igneous rock invading an older rock ISOCLINAL Applied to folds in which the limbs are practically parallel 
JOINT Rock fracture 
LACCOLITH Sill-like intrusion which has domed up the overlying rocks 
MESA Flat topped, cliff bound mountain 
METAMORPHIC Applied to rocks which have been formed by the effect of heat, pressure etc on existing rocks 
MIDDEN Aboriginal refuse heap 
MOLLUSC Marine organism characterised by a fleshy foot MONOCLINE Local steepening of the dip of strata  
NORMAL FAULT Displacement of strata resulting from tension within the rock 
OROGENIC Mountain building 
OUTLIER Body of rock surrounded by older rocks, produced by erosion 
OXIDISED As applied to ore bodies, the uppermost, weathered region 
PALAEONTOLOGY Study of former life as revealed by fossils PHENOCRYSTS Relatively large crystals in an igneous rock, usually ones which crystallised earlier 
PLUTONIC  Formed deep within the earth 
POLYZOA Group of marine, colonial organisms 
PORPHYRY Igneous rock containing phenocrysts PSEUDOMORPH Crystal produced by the alteration or replacement of another mineral, but retaining the original shape PYROCLASTIC Applied to sediments produced by explosive volcanic activity 
RACE Channel cut to convey water, usually for alluvial mining REVERSE FAULT Displacement of strata caused by compression within the rock 
SEDIMENTARY Applied to rocks deposited in layers SERPENTINE Rock forming minerals frequently derived from the alteration of ferromagnesian minerals 
SILICIFIED Replaced or cemented by silica 
SILL Body of igneous rock forced between strata 
SINK HOLE Depression caused by solution in a limestone body SLUMP Sediment that has moved down a slope, causing disturbance of the original bedding 
SPHEROIDAL WEATHERING Type of weathering which causes outer layers to peel off, forming rounded boulders 
STACK Small coastal island not yet removed by marine erosion STRATIGRAPHY Study of layered sedimentary rocks STRIATIONS Subparallel grooves, sometimes caused by glacial movement 
STRIKE Course or bearing of an outcrop, usually applied to sedimentary rocks, dykes, veins etc 
SYNCLINE Fold in which strata are arched downwards TECTONIC Applied to the deformation of the Earth’s crust TERRACE Benches produced by deposition and erosion of sediment 
TOPOGRAPHIC Term applied to the surface relief of the Earth TUFF Fine grained pyroclastic material 
TWINNING Tendency of crystals, when growing, to share faces, edges etc 
ULTRABASIC As applied to igneous rocks, containing less than 45% SiO2 by analysis 
ULTRAVIOLET RADIATION Rays lying outside the violet end of the visible spectrum 
UNCONFORMITY Erosional surface separating younger and older rocks; a time gap 
VESICULAR Containing small gas cavities or vesicles 
VUGH Cavity in a rock frequently lined with crystals 
WASHOUT Channel cut through sediment which is later filled in itself 
WATER TABLE Surface below which rock openings are filled with water 
XENOLITH Applied to foreign rock material found within a body of igneous rock 
Volcanic Agglomerate Bombo December 1968

Thursday, 18 July 2019

FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 23): THE CLYDE RIVER VALLEY


 Taking 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 Nowra Sandstone or sometimes part of the Berry Formation, with cliffs of lower units below this level. 
The basement rocks are of presumed Ordovician age, flanked on the west by the Devonian group near Currockbilly. There has been some mineralisation and gold has been won from many places near Bateman’s Bay and Nelligen. Some copper and lead prospects have also been recorded. 
This chapter deals mainly with places accessible by road. The numerous bushwalks based on Yadboro have not been treated since they are taken by relatively few tourists. Only the Pigeon House has been included, partly because of its historic and romantic interest, but also because its geology is typical of all the sandstone peaks. 
Excursion 15a 
Yadboro and Pigeon House Mountain (34 miles return) 
Captain Cook sighted Pigeon House Mountain (the Pigeon House or Pigeon Top) on April 21st 1770. At first it was mistaken for a distant island, as only its sandstone cap could be seen. The ‘Endeavour’ was probably off Moruya at the time. Its identity was established the following day and its name given because it resembled the dovecotes familiar to Cook in England.  
Route: Termeil-Boyne Creek-Pigeon House-Yadboro 
Turn right off the Prince’s Highway along Woodburn Road, 4 ½ miles south of Lake Tabourie. 
One mile from the highway, the road crosses a small inlier of slate, which may be examined on the left of the road. For the next mile the road climbs through the lower Conjola Formation and extensive outcrops of siltstone may be seen near the crest of the range. This probably corresponds to the silty member at Point Upright. The highest point in this area, Boyne Trig., is capped by sandstone and this is possibly equivalent to the outcrops at Crampton Island, Bannister Point, and Jervis Bay. 
Turn left on the Brooman road 3.4 miles from the Prince’s Highway and right on the Yadboro forestry road 2.3 miles further on. The base of the Permian is not very noticeable and the road passes over slate country northwards towards the Pigeon House. Stop at Boyne Creek, 4 miles along the Yadboro road. 
Stop 1. Slate is the dominant rock type in the creek gravel, with lesser amounts of quartzite and conglomerate. Boyne Creek possibly carries alluvial gold in small quantities. This creek is the last good place for obtaining drinking water before the ascent of the Pigeon House.  
Continue towards Yadboro. Park on the left where the Pigeon House track leaves on the right, 2.3 miles from Boyne Creek. 
Stop 2. This area was burned out late in 1968 and the road towards Pigeon House became impassable. Before then, it was possible to drive one mile towards the mountain. The vehicular track ends at the bottom of a steep slope, at an elevation of 750 feet. The only rock outcrops at this level are of slate, intersected by quartz veins. 
At the top of the steep slope, the base of the Shoalhaven Group outcrops at 1,200 feet. The Yadboro Conglomerate, full of slate fragments, is the lowest member at this point. Skirt the cliff to the left and climb to the plateau above a few hundred yards further on. By now a fine view of the mountain, a little over a mile ahead, will have opened out. The other prominent sandstone peaks and the Budawang Range have also come into view. 
Outcrops of the Conjola Formation persist towards the base of the mountain until the Wandrawandian Siltstone is reached at a height of 1,700 feet. Fossils occur in this and the lower part of the overlying Nowra Sandstone. Climb up to the base of the sandstone and around the left side to the northern end. The route to the summit (2,361 feet) is clearly marked and involves scrambling up several steep pebbly slopes and scaling a few wooden ladders in the more difficult places. The view is as comprehensive as any in NSW. Perhaps the valley of the Clyde River, immediately to the north commands the greatest attention.  
The entire walk from the road and the return journey takes 4-5 hours. The climb is not difficult except for the final pyramid of sandstone, which would daunt the average hiker. 
NOTE: This is the only place in this work where I think a comment on developments since it was written is essential. In 1971 I led a group of students from Erina High School to this spot. The old route to the summit had been superseded by a set of steel ladders and the track was more clearly marked. This made it possible for many who would have baulked at the old ascent to reach the summit. 
Continue on to Yadboro, where the Clyde River is reached, 6 miles beyond Boyne Creek. 
Stop 3. When subsidence began early in the Permian period (or perhaps the late Carboniferous period), this area was the first to be seriously affected. The earliest sediment to be deposited, the Pigeon House Creek Siltstone, is found only in the neighbourhood of Yadboro, as is the overlying conglomerate. Later on, the whole area west to the Budawang range began to subside and the rest of the marine beds accumulated.  
Yadboro is the centre from which numerous bushwalks radiate. The Clyde River itself may be followed upstream on the eastern side of the bridge. The road across the bridge leads into a network of timber tracks. Yadboro Creek, the western tributary of the Clyde in this area, carries rhyolite and the Devonian rocks derived from the Budawang Range exposures. 
The Clyde River valley from the summit
 of the Pigeon House January 1969 

The Castle from the Yadboro Road
October 1967
Excursion 15b 
Brooman, Nelligen and the Lower Clyde (51 miles) 
Ordovician basement rocks form the surface over the entire lower Clyde valley. This is an area of extensive gold mineralisation, one where many lonely prospectors hoped to strike it rich but few succeeded. 
Route: Milton-Brooman-Shallow Crossing-Brimberamala-Currowan Creek-Nelligen  
Take the Nelligen road from Milton, as in Excursion 12b. Fine views of the Pigeon House are seen 10 miles south of Milton. Note the contrast with the hills of Devonian rocks in the background. The road from Termeil is passed on the left 13 miles south (see Excursion 14a). Shortly after, the sandstones are left behind and the slate is seen for the first time. Any creeks from here on could yield alluvial gold. 

Brooman, 21 miles from Milton, was the site of a minor gold rush, which led to very little gold being found. The Clyde River presents a very fine appearance alongside the road. Stop at Shallow Crossing, 7 miles from Brooman, where a concrete causeway fords the river. 
Stop 1. Alluvial gold has been dredged from the Clyde in this vicinity, but the amateur prospector cannot hope to find much in a place like this. The gravel in the river includes slate, quartzite, and rhyolite, the latter having come down via Yadboro Creek. 
Turn right along Mare’s Hill fire road, ½ mile south of Shallow Crossing. Take the right branch 4.2 miles further on. Stop at the old mullock heaps by the roadside 0.8 miles north. 
Stop 2. The Brimberamala mines were good small scale producers many years ago. This area is dotted with numerous mine dumps and pitted with shafts. The creek carries alluvial gold, which undoubtedly led to the discovery of quartz reefs on this hill side. Some of the slate shows the interesting effects of extreme folding. 
Either return to the Nelligen road the same way, or turn right from the Brimberamala road and follow the main roads back to the Nelligen road further south (5.6 miles). 
From Currowan Creek, the road passes through pleasant wooded country alongside the Clyde River until the Braidwood road is reached 7 ½ miles further on. 
Stop 3. The slate here is seen to be isoclinally folded and numerous small faults and fold axes can be detected. Quartz veins run through the whole mass. 
At Nelligen the Clyde River is crossed by a fine new bridge replacing the old ferry which formerly operated here. The Prince’s Highway at Bateman’s Bay is 5 
miles further on (see Excursion 13c). 

Pigeon House Mountain from the
Brooman Road September 1967
Granite-slate contact on the Clyde Mountain
road September 1967 

Questions 
1. Give an account of the formations met with between Boyne Creek and the summit of the Pigeon House. 
2. Explain the existence of numerous sandstone outliers in the upper Clyde valley. 
3. Suggest reasons why the Clyde River parallels the coast before turning east near Bateman’s Bay. 
4. Granite occurs a few miles west of Nelligen. Relate this fact to the occurrence of gold in this area. Why is gold uncommon in the older rocks north of Brooman? 
The Clyde River ferry at Nelligen October 1963 


Tuesday, 16 July 2019

FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 22): THE NERRIGA DISTRICT

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The Permian sediments reach their highest level east of Nerriga and it is in this area that spectacular examples of erosion are most common. 
Extensive denudation has exposed the underlying basement rocks over a wide area. These are a continuation of the rocks exposed at Yalwal and Ettrema in the north. 
The Budawang Range reaches a height of 3,711 feet at Currockbilly Mountain and a similar height at Mount Budawang a little further south. This prominent ridge is the backbone of the basement, consisting essentially of a narrow belt of resistant Devonian strata flanked by Ordovician slates. Marine fossils occur in both these groups as well as sporadic mineralisation. Alluvial gold has been extensively mined, but reefs have rarely proved profitable. 
The core of the area described in these pages is a wild confusion of deep valleys and remarkable sandstone peaks. It is a place to be seen only by the bushwalker and not for the ordinary tourist. It is beyond the scope of this book to describe any but the most accessible places, but the geological features of these are representative of the whole. 
Excursion 14a 
Quilty’s Mountain (18 miles return) 
From Sassafras, a road runs south towards the Clyde River. It provides access to many fine views of the Clyde and its tributaries. Quilty’s Mountain is remarkable for its aboriginal Bora Ground, one of the few reminders of the former inhabitants of this district. 
Route: Sassafras-Round Hill-The Vines-Quilty’s Mountain 
Turn left from the Braidwood road 1 mile past Stony Hill and 34 miles from Nowra (see Excursion 9a). 
For the first mile, the road crosses basalt country, outcrops of which may be examined in many places. Thereafter, the sandstone-basalt boundary is crossed several times and great contrasts in their respective vegetations can easily be seen. 
Some 3.7 miles from Sassafras, a view to the east opens up, including the Tianjara mesas. The uppermost part of the Clyde gorge lies in between, a short distance to the east. Stop at Round Hill, a prominent residual beside the road a little further on. 
Stop 1. The sandstone outcropping here is typical of the Berry Formation in this area. It resembles that seen at Stony Hill and Tianjara. From the summit (2,412 feet) there is a panorama of the Clyde gorge, the Endrick River, and the mountain ranges in the south. Mt Talaterang and the top of the Pigeon House are also visible. 
A little further south the road skirts Newhaven Gap which provides access to the Clyde canyon, emerging upstream from the Coal Measures exposures (see Excursion 11a, Stop 4). The road reaches its closest point to the gorge 2.2 miles south of Round Hill. 
Stop 2. The cliff edge is only a few minutes walk from the road. There are numerous open joints in the sandstone, some of which yawn like great caves well back from the cliff and provided a convenient disposal unit for the sawmill which formerly operated here.  
It is possible to descend into the valley by way of some of the more accessible joints. Far below, the base of the Permian sediments is marked by a prominent bed of sandstone, below which outcrop the slates of the basement.  
The road deteriorates past this point and the next 2 miles should be covered on foot. Basalt is reached after the track has descended a wide gap in the sandstone plateau. Shortly afterwards, the track swings to the north. 
Stop 3. This locality, known as The Vines, is covered by thick vegetation, in contrast to the scrubby sandstone country nearby. A narrow belt of basalt may be traced northwards into the valley of the Endrick River as far as Nerriga. Apparently the lava flowed down the valley in earlier times from a point south of The Vines and since then the Endrick River has removed most of it by erosion. 
Quilty’s Mountain (or Mount Endrick) lies just west of this point. A track ascends to the bare rock outcrops near the summit, where aboriginal motifs in the form of native animals are depicted on the ground by heaps of small stones. This locality should be treated with all the respect it deserves as a historic monument and none of the stones should be moved. 
From The Vines, the track may be followed to Nerriga (12 miles). Otherwise, the return journey must be made over the same route. 

Excursion 14b 
Nerriga-Braidwood (68 miles) 
The Permian sediments reach their western limit at Nerriga and their present boundary with the basement rocks trends towards the coast, reaching it at Bateman’s Bay. On this excursion, outcrops of Upper Ordovician and Upper Devonian rocks are prominent and occupy most of the surface. 
Route: Nerriga-Oallen-Corang River-Charley’s Forest-Mongarlowe-Braidwood 
This excursion begins where Excursion 9a finishes – at the western edge of the sandstone plateau, east of Nerriga. The base of the Nowra Sandstone is easily found. The unconformity with the Ordovician basement is 0.7 miles further down the hill at a point where the road bends to the right. 
Stop 1. There is no marked unconformity visible as such, but there is a distinct change of slope and in vegetation at this point. The basement rocks consist of quartzite and phyllite intersected by numerous quartz veins. 
From this point on, the road descends more steeply and soon the Endrick River is reached. Cars may be parked on the left just before the bridge. 
Stop 2. The river gravel is representative of the rocks upstream and of no particular interest. The road cutting, however, reveals an interesting section of steeply dipping slates, with many quartz veins, overlain unconformably by semi-consolidated river gravel. This strongly resembles that in the nearby stream and is plainly of recent origin. Notice its irregular base, representing part of the old river bed. 
The Clyde River gorge from
near Newhaven Gap April 1969 
From the Endrick River, the road ascends to a comparatively level, fertile area underlain by the same Tertiary basalt seen at The Vines (see Excursion 14a, Stop 3). Outcrops may be seen on the right 0.6 miles from the river. Silicified logs are known to occur beneath the basalt west of the road and enquiries at nearby farmhouses should yield further information. The Endrick River drops over a large waterfall just beyond these paddocks and copper minerals have been found in the gorge below. 
Continue through Nerriga and turn right along the Goulburn road 2 miles past the town. This road passes through an area where alluvial gold was once extensively mined. Jerricknora Creek was one of the chief centres, especially towards its confluence with the Shoalhaven River. Stop where some old mine heaps may be seen on the left, 5 miles from the Braidwood Road. 
Stop 3. A series of shafts on the hill side mark the outcrop of a quartz reef; quartz and slate are plentiful on the heaps. Alluvial gold found in the nearby creek was probably traced to this outcrop. Similar small mines abound in the area, but most of them are of little interest. 
Continue to the Shoalhaven River at Oallen Crossing
Stop 4. This is a favourite place for fossicking. Gold may be panned from gravel in the river itself or from the extensive gravel deposits alongside the road just before the bridge. There is nearly always someone here to give advice about the best places to try! 
From Oallen, the road may be followed on to Bungonia (26 miles) and thence to Bungonia Caves (see Excursion 9c). Otherwise, the road should be retraced to Nerriga (7 miles) and then right towards Braidwood again. Stop at the Corang River 5 miles further on. 
Stop 5. Some alluvial gold may be washed here. The river gravel consists mainly of the local low grade metamorphic rocks with some pieces of Permian conglomerate. A ½ mile past the bridge the road crosses the remains of an old water race. Built in the 1890’s, this channel carried water 24 miles from the upper Corang River through tunnels and across bridges to supply a head of pressure for the hydraulic sluicing of gold bearing gravels. The race is visible for miles upstream from the bridge. 
New road cuttings south of the Corang River reveal good exposures of steeply dipping slate. Blocks of red jasper occur 2 miles south and in this vicinity there are many outcrops of old river gravel. 
Turn left for Mongarlowe 2.7 miles beyond the river. The road crosses Wog Wog Creek and begins to climb slowly. Outliers of Permian sandstone may be seen a mile or so to the east. Stop at a gate on the left 2.4 miles from the creek. It is possible to drive a short distance along this track. 
Stop 6. Access may be had from this point to the Corang group of outliers and the underlying Upper Devonian strata. The track leads down to a creek crossing and shortly after a branch leads up the hill to the right. Outcrops here are mainly of slate. About ½ mile from the creek, the first Devonian rocks are met. These are rhyolites and they form a narrow belt a few hundred yards across. Much of the rhyolite is silicified and has become masses of chalcedony containing cavities filled with small quartz crystals. Common opal also occurs. 
Beyond the rhyolite, beds of sandstone strike north-south across the track. These dip steeply to the east and are intersected by numerous quartz veins. They belong to the Upper Devonian Merimbula Formation and marine fossils have been found in the sandstone in this vicinity. The location is to the right of the track, 400 yards beyond the rhyolite boundary.  
Should it be desired to climb Corang Peak, the track must be followed for another ½ mile before a left branch is taken towards the mountain. Corang consists largely of the Nowra Sandstone. The Yadboro Conglomerate forms the lowest outcrops of the Permian here. The view south from Corang reveals Wog Wog Mountain in the near distance with Currockbilly beyond. The axis of the Budawang Range is essentially that of a syncline in which the Devonian rocks have been preserved. Quartzite ridges are prominent along the range and form the highest points. 
Return to the Mongarlowe road. Some 2.2 miles further south, First Curradux Creek is crossed. Stop just before the second crossing where there is a small roadside quarry on the left. 
Stop 7. Steeply dipping beds of black siltstone contain Upper Ordovician graptolite fossils. These are confined to one narrow zone in the middle of the quarry, where the rock is fairly soft and quite fissile. It is interesting to speculate on the sparseness of fossil evidence in these ancient rocks. Without these rare discoveries, the age of these beds would be only vaguely known. Do not remove, from this or any other place, any fossil material for which you have no use. 
Occasional pieces of agate may be found in the creek, brought down from rhyolite outcrops a short distance upstream. Continue towards Mongarlowe. Good views of the Budawang Range and Corang are seen a little further south. Notice the thin vegetation on this side of the range. The coastal side is much more thickly clad, presumably because of its higher rainfall. 
Stop at a roadside quarry a little over 3 miles further south, near Charley’s Forest. 
Stop 8. Greenish altered rhyolite and shale outcrop here. It is possible that the rhyolite has been faulted against the Ordovician slates here, as a considerable area of quartz occurs near the boundary just north of the road. 
Eight miles south of Sapling Yard Creek, the road passes through Mongarlowe. This was once a prosperous gold mining centre and the Mongarlowe River was extensively dredged.  
The left branch of the road leads to Monga and Clyde Mountain, while the right goes to Braidwood (8 miles). On the Monga road there is much evidence of former mining activity. The Braidwood road passes onto granite 5 miles from the town, from which point on there is a marked change in topography and vegetation. 
Questions 
1. Discuss the changes observed in the topography when passing from (a) basalt to sandstone at Sassafras, (b) sandstone to slate at the Endrick River and (c) slate to granite near Mongarlowe. 
2. Put forward theories to explain the joints seen in the sandstone near the edge of the Clyde gorge. 
3. What evidence is there to suggest that there has been volcanic activity in the Endrick River area since the uplift of the country began? 
4. Compare the shapes of Corang Peak and Currockbilly. What has caused this essential difference? 
5. What observations could be used to distinguish an outcrop of Upper Devonian sandstone from a Permian one? 
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FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 21): THE TERMEIL AND DURRAS DISTRICTS

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. 
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FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 20): THE MILTON-ULLADULLA DISTRICT

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 progress. 
Excursion 12a 
Milton-Ulladulla (17 miles) 
Included in this excursion are splendid exposures of the Milton intrusion, richly fossiliferous Permian sediments, and Tertiary Volcanics in the form of dykes and flow remnants. 
Route: Yatteyatah-Little Forest-Milton-Ulladulla-Mollymook-Bannister’s Point-Narrawallee-Milton 
The excursion commences at the junction of the Prince’s Highway and the Porter’s Creek Dam road. The road south skirts the edge of a northerly part of the Milton intrusion. A diversion may be made to Lake Conjola entrance, by turning left 1 mile south. Silica has been quarried in that area. 
Through Yatteyatah, the road descends to the lush pastures of the Milton district. At first the road crosses alluvial soils, but shortly after reaches outcrops of monzonite. Stop where the rock is exposed in a deep cutting. 
Stop 1. The rock here is rather weathered and better specimens may be obtained on nearby hillsides. The entire Milton intrusion varies greatly, in places (as here) resembling dolerite while elsewhere it grades into more typical monzonite or even trachyte. 
Turn right along Little Forest Road, half a mile further south. The road soon leaves the intrusion and continues towards the Little Forest Plateau through poorer country. Three miles from the highway, turn right. The road then descends to Little Forest Creek. 
Stop 2. Another small exposure of Ordovician slate is exposed here. The unconformity may be examined by walking up the road on either side of the creek until slate is replaced by sandstone. Upstream, a small inlier of the Coal Measures may be found by following the creek for half a mile. Beyond Little Forest Creek, the road rises sharply onto that part of the intrusion seen from the Rotary Lookout (see Excursion 11a, Stop 7). 
Return to the highway. One mile further south the road climbs sharply through monzonite. Stop where a small quarry is seen on the left towards the top of the hill. 
Stop 3. The rock here is fairly typical of the intrusion, being a variety of porphyritic monzonite. The large felspar phenocrysts are noteworthy. The rock face also displays a number of aplitic and pegmatitic veins.  
The view to the west shows the level Nowra Sandstone horizon behind Little Forest, with the Tianjara mesas further north. Mt Kingiman blocks the view towards Pigeon House in the south west. 
Continue through Milton towards Ulladulla. The Nelligen road (Excursion 12b) is marked by a sign pointing to the blue metal quarries. 
Stop at a point 2.2 miles further south, just before Mollymook. 
Stop 4. Olivine basalt, part of a flow remnant, occurs here in the road cutting. It is very weathered and good examples of spheroidal weathering may be seen. Building excavations nearby in Mollymook have revealed large masses of resinous opalised wood beneath the basalt. These appear to have been logs buried beneath the flow and thus preserved. Any new excavations in this locality are worth checking for further occurrences. 
Continue towards Ulladulla. Stop along the waterfront where a large tourist map has been erected. 
Stop 5. Ulladulla Harbour may have been formed by the erosion of a number of east-west dykes, traces of which have been found at the northern end of the beach. It has become a haven for fishing craft and is the safest anchorage between Jervis Bay and Bateman’s Bay. 
Warden’s Head lighthouse may be reached by passing through the camping area or by following Deering Street, which turns left at the top of the hill through Ulladulla. The lighthouse is approximately one mile east of the highway. 
Stop 6. Warden’s Head is a well-known collecting ground for Permian fossils and a whole day could be spent here. A track descends to the rock platform a little south of the lighthouse. From the cliff top, observe the prominent north-south strike of the strata below, which has led to the formation of bomboras just off the platform. The sediments, mainly siltstone, dip towards the west at this point, but there is a considerable local variation in this. 
Fossils at Warden Head
November 1963
At the point where the track reaches the rock platform, the beds are much disturbed. A small clastic dyke may be seen a few feet to the west and there is abundant evidence of slumping within the siltstone. Fossils may be found in the rocks to the south but more especially to the north.  If time permits, walk right around to Ulladulla harbour. Spherical concretions (cannonballs) occur here and there are several glendonite beds, resembling those at Huskisson and Crookhaven. The sediments are richly fossiliferous and the superabundance of fossils has made some of the beds into impure limestone. Some of this proves to be largely made of the spines of small brachiopods, such as Stropholosia and Terrakea. 
Return to Ulladulla. The return trip to Milton may be made by way of Mollymook, Bannister’s Point and Narrawallee. At Bannister’s Point, silica has been quarried extensively. A large dyke occurs near the ruined jetty on the northern side of the headland, and this seems to be the origin of the quartz solutions which formed the quartzite. The sandstone at Bannister’s Point has a prominent easterly dip, which can be clearly seen from the road. 

Excursion 12b 
Milton and Burrill Lake(20 miles) 
This excursion includes features similar to those covered in the previous one, with the addition of several large dykes and scenic mountain areas. 
Route: Nelligen road from Milton, thence via the Wheelbarrow Road to the Prince’s Highway at Lake Burrill and return to Milton. 
From Milton, the Nelligen road goes south across the monzonite for 4 miles. Good views of the Little Forest Plateau, The Castle, Mt Kingiman, and the top of the Pigeon House are to be had near Milton. Stop at the blue metal quarries, 5 miles from Milton. Request permission to enter. 
Stop 1. The quarry being worked to the right of the road exposes a pale porphyritic monzonite, rather different to that seen at Milton. There are few veins or cavities and the jointing is irregular. The older quarry, on the left a little further south, shows considerable variation in the rock fabric. Much of it has been serpentinised, evidently by solutions rising from below. Most of the rock is finer grained than that seen in the other quarry, apparently because it is nearer the edge of the intrusion. Labradorite phenocrysts, however, are still plentiful. 
Just past the quarries, a view of Burrill Lake reveals a small delta at its northern end. Lakes Conjola and Burrill are both examples of drowned valleys. A little further on, the road passes onto the Conjola Formation and outcrops of sandstone may be seen in road cuttings and in a quarry beside the road. Three miles past the monzonite quarries, the road to Mt Kingiman branches to the right. 
Diversion 1. Some 1.6 mile along this road, there is a further branch. The left branch leads to Jindelara Creek and the right to Mt Kingiman. Keep to the right branch. The road climbs steadily. Outcrops of the Wandrawandian Siltstone may be seen after 1 ½ miles and loose blocks of Nowra Sandstone beyond this. The road skirts the western edge of the mountain for a further 1 ½ miles before becoming impassable. At any suitable point, the sandstone ridge above may be climbed, from which superb views of Milton, the Pigeon House, and the Little Forest Plateau may be obtained. 
Return to the other branch and turn right. Stop at an old bridge 1 mile further on. 
This area was burned out by severe bush fires in 1968 and the bridge was badly damaged. Immediately below the bridge is a fine waterfall, flowing over sandstone of the Conjola Formation. The track ahead may be followed to the Pigeon House. Take the left fork near Jindelara Creek 1 ½ miles ahead. The distance from the fall to the summit is about 5 ½ miles. Return to the Nelligen road and continue in a southerly direction. Turn right 1.3 miles further on. 
Diversion 2. This road leads to a group of small farms situated on part of the Termeil Essexite intrusion (see Excursion 13a). This area drains into Boyne Creek which probably carries alluvial gold similar to that found on Murramarang Beach. 
Views of the Pigeon House are frequent along this road. Turn left just past a bridge after 1.3 miles. Shortly after, cleared country is reached and essexite boulders are plentiful. Return to the Nelligen road. Turn right along the Wheelbarrow Road, which descends to the Prince’s Highway near Burrill Lake. Turn left along the highway and right to Dolphin Point just before the bridge over the lake. This leads out to the coast south of Burrill Entrance 
The coast from Burrill Entrance south to Lagoon Point has many features of interest. 
The rocks are principally siltstone and sandstone of the Conjola Formation, and closely resemble the outcrops at Warden’s Head, 4 miles to the north. They contain numerous fossils and exceptionally large erratics composed of all kinds of metamorphic rocks. 
Two large porphyritic dolerite dykes strike east-west across the rock platform about 500 yards south of the entrance. Both have arched up the intruded rocks in a similar fashion to the Berrara dyke. The northern dyke has a width of 45 feet and the southern 120 feet, making it one of the largest recorded dykes on the south coast. There is a very marked bleached zone on both sides of these dykes, where the igneous rock has been altered by solutions derived from the sedimentary rocks. 
Schist erratic January 1966
Further south, a number of erratics project prominently from the surface of the platform. Some of these are composed of highly contorted quartzite, others of granite and of intermediate volcanic rocks. They are known to bear some resemblance to the rock types still outcropping south west of the Sydney basin towards Canberra and they may have been brought from that direction. 
Glendonites and concretions occur in the siltstone south towards Lagoon Point (1 mile from the large dyke). Good examples of marine fossils are abundant along the shore and some fine examples of crinoids have been found in this area. 
Questions 
1. Is there any evidence to support the suggestion that the Milton intrusion is older than the Shoalhaven Group? Give support for the contrary view. 
2. Give an account of the origin of the sedimentary structures seen at Warden’s Head. 
3. Construct a geological history of the Milton-Ulladulla district. 
4. Discuss the petrology of the Milton intrusion, using data gained from the outcrops studied on these excursions. 
5. The base of the Nowra Sandstone stands at 1,500 feet near Little Forest, 2,100 feet at the Pigeon House but only 1,200 feet at Mt Kingiman. Suggest reasons for this situation.  
Mollymook Beach January 1958
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