FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 10)
Chapter 5: Kangaroo Valley
The Cambewarra Range effectively seals in one of Australia’s scenic gems – Kangaroo Valley. Like any other impressive piece of nature’s handiwork, people have ascribed its origin to anything but the simplest of causes. Since 1818, when white men first entered the “Kangaroo Ground”, as it was then known, there have been numerous suggestions to explain its existence. It has been described as a ‘picturesque sunken valley’, the implication being that its present form is the result of subsidence. Others have thought that it represents a former lake, or that volcanoes led to its formation. The truth is that the Kangaroo River and its tributaries have carried away the products of erosion over a period of many thousands of years, leaving the framework of the rock structure exposed as we see it today.
Volcanic rocks belonging to the upper Berry Formation are mainly confined to the eastern half of the valley and by their weathering have released the quartz minerals which are well know to most visitors. Being more resistant than other local rocks and minerals, these have accumulated in the river and streams, where they are eagerly sought today.
The story of the rocks themselves is the same as that outlined in the previous chapters. Their exposure in the valley is the result of uplift and erosion on a large scale. The Kangaroo River, like its neighbour the Wingecarribee to the north, flows to the west, away from the coast. In earlier times, before the present Shoalhaven gorge was carved, drainage probably continued to the west and into the upper Wollondilly River. However, streams draining to the east captured this part of the Wollondilly system incorporating it into the present Shoalhaven drainage basin.
Excursion 5a
Kangaroo River and Barrengarry (75 miles)
Most of the valley is included in this excursion. The rock types range from the Devonian basement up to the Hawkesbury Sandstone and special attention is paid to the occurrence of semi-precious stones.
Route: Cambewarra Lookout-Fitzroy Falls via Kangaroo Valley (with diversions to Yarrunga Creek and Upper Kangaroo River)
Stop 1. The view from Cambewarra Lookout shows the dependence of scenery on the underlying geology. Immediately below the lookout lie steep sandstone slopes and the forest clad outcrops of the Gerringong Volcanics. The cleared land is underlain either by Berry siltstones or alluvial deposits. Outcrops of sandstone near Bomaderry and Nowra show up by virtue of the bushland remaining uncleared in their vicinity. Most prominent of all are the swamps and watercourses of the lower Shoalhaven River, described in Chapter 3. Other features easily recognisable include Coolangatta Mountain, Nowra Hill, and Jervis Bay. It is worth the trouble trying to locate geological boundaries from a vantage point such as this. It is the next best thing to an aerial view.
Stop 2. (See Stop 4, Excursion 4b) In Kangaroo Valley, clearing has been largely confined to the Berry Formation below the Budgong Sandstone, which forms the lower line of cliffs. Across the valley in the distance lies the fertile Robertson district, where better soils derived from Wianamatta shales and Tertiary volcanics contrast with the poor sandstone soils seen on Cambewarra Mountain (to the left of this point).
Take the road into the Valley. Outcrops of the Cambewarra Flow are soon succeeded by red tuffs and dark siltstone. Good exposures are rare. Fragments of coal and pieces of petrified wood and jasper may be found in any of the creeks draining from Cambewarra Mountain above the road. Excursion 5b begins at the Berry road, 3.7 miles from Stop 2. Nugent’s Creek (4.7 miles) has yielded fine specimens of agate and jasper. Excursion 4b terminates at the Mt Scanzi road, just past Kangaroo Valley township. Stop at the Hampden Bridge over the Kangaroo River.
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| Hampden Bridge Kangaroo Valley January 1960 |
Stop 3. This bridge, opened in 1898, is the landmark of the Valley. It replaces an earlier wooden structure, rather like the one across Yarrunga Creek at Fitzroy Falls.
Just above this spot, the river enters a narrow sandstone gorge, which is spanned picturesquely by the suspension bridge. It must not be thought that the presence of such a gorge in the valley floor is the result of uplift and rejuvenation of the stream. It is merely the expression of the Nowra Sandstone at this point, whose cliff forming tendencies have prevented the widening of the valley. Similar gorges occur where the river intersects the other resistant strata in the sequence, notably the Hawkesbury and Budgong Sandstones, and the Conjola Formation.
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| Kangaroo Valley April 1969 |
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| Hampden Bridge January 1960 |
The sandstone, while being similar to the Nowra Sandstone elsewhere, is not noticeably fossiliferous here, but a careful search may reveal some fossils. Most visitors are interested in finding specimens of petrified wood, jasper, and agate in the river gravel.
At such a popular picnic ground as this, the chance of finding good specimens is small, except after a flood when a fresh surface of gravel has been exposed. Other rock types found here include coal and the Cambewarra latite, brought down from further up the valley. Quartz minerals may be found all along the river, but permission should always be sought before entering private property. This area has been a hunting ground for such specimens for many years and good material is becoming scarce.
Continue towards Moss Vale. Diversions up and down the valley may be made to Bendeela and Upper Kangaroo River within half a mile of the bridge.
Diversion 1. Bendeela, Yarrunga Creek and Meryla Pass.
Turn left a short distance beyond Hampden Bridge. For 2 miles the road passes over sandstone and occasionally siltstone. Some 1.7 miles from the main road, a branch to the right continues along the level of the base of the Berry Formation for several miles. Fine views of the valley walls are to be had from this junction, Berry Mountain, Cambewarra and Mt Scanzi being prominent. Shortly after, the road passes down through the Nowra Sandstone into the Wandrawandian Siltstone. The Kangaroo River emerges from its gorge nearby and the road follows its meandering course for a further 4 miles before branching.
The right hand branch first ascends the side of the valley then descends to Yarrunga Creek, 12 miles from Hampden Bridge. Sandstone of the Conjola Formation outcrops here, but Devonian quartzite and conglomerate outcrop in the river bed 1 mile below the ford.
The Yarrunga Dam, part of the MWS&DB’s Shoalhaven Scheme, will be built across the Kangaroo River downstream of its junction with Yarrunga Creek. It will be a 125 feet high concrete gravity dam, with an associated underground pumping station designed to lift 600 million gallons of water a day through a height of 2,200 feet, for storage near Fitzroy Falls.
Beyond Yarrunga Creek, the road deteriorates and is probably untrafficable for most vehicles coming from this direction. It is approximately 7 miles to the top of Meryla Pass and the road passes through a fine section of strata right up to the Hawkesbury Sandstone. From the top, a road may be followed to Moss Vale; otherwise the route from Kangaroo Valley must be retraced.
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| View from the top of Meryla Pass June 1972 |
Diversion 2. Upper Kangaroo River.
Turn right ½ mile beyond Hampden Bridge. This road leads to farms scattered along the upper part of Kangaroo Valley and may be followed for 7 or more miles before a return journey must be made along the same route. The rocks exposed along the road are all siltstones of the Berry Formation while high above the road may be seen the continuous cliffs so typical of Kangaroo Valley. Most visitors are interested in collecting stones from the river gravel and this may be done with caution at many places.
Barrengarry Creek is crossed soon after leaving the Moss Vale road. The gravel is deficient in volcanic rocks, since the flows of the Gerringong Volcanics barely reached into the area within its catchment. Otherwise, the fragments of coal, sandstone etc reveal that the geology is similar to that seen elsewhere in the valley.
Roadside quarries may be examined at points 1.4 and 4.4 miles past Barrengarry Creek. The rock is a typical siltstone, containing occasional marine fossils and displaying spheroidal weathering.
A road branching to the right 1.5 miles further on fords the river and then follows the valley of Geringong Creek for about 1 mile. The river and the creek here yield occasional specimens of agate, green and red jasper, and boulders of fossiliferous Budgong Sandstone, brought down from higher up.
The little community of Upper Kangaroo Valley is marked by its church, school, and hall. Beyond this point, the valley begins to narrow and farming land becomes more precipitous, although there are farms for more than 3 miles above Geringong Creek. Timber roads provide access to the higher slopes and some of these have been connected with roads leading south from Robertson, only a few miles away.
Return to the Moss Vale road and turn right towards Barrengarry Mountain. The ascent begins 2.6 miles further on. The first bend to the left reveals a typical exposure of Berry siltstone. About 1 mile further on, it is possible to park on the roadside at a sharp bend backed by a sandstone cliff.
Stop 4. This is the Budgong Sandstone and it is noticeably different from the Hawkesbury Sandstone seen higher up. It will be recalled that it is the equivalent of the Broughton Sandstone, which is highly tuffaceous, in the eastern part of the valley. There is still a small tuffaceous element in this sandstone, but it has lessened considerably because of the distance from the Gerringong Volcanic centre.
There are few good outcrops higher up the mountain. Steeply dipping sandstone is seen at a sharp bend on the left 1.4 miles beyond Stop 4. This may be due to folding or faulting of the strata, or merely to the overturning of a large block of sandstone during erosion. The cause is not immediately apparent.
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| Kangaroo Valley from Manning's Lookout June 1972 |
Turn right to Manning’s Lookout, 8 miles from Hampden Bridge.
Stop 5. A clear view of the valley with its many geological features is seen from this lookout. The two sandstone cliff lines are clear enough. Notice how there has been less clearing on this side of the valley. The Berry Formation contains a much higher volcanic fraction on the eastern side, so the soils derived from it are more fertile.
The Hawkesbury Sandstone here is at the same level as at Good Dog Mountain. What a vast amount of rock has been carried away by erosion in between! Cross bedding, pebble beds, and prominent open joints may be examined here, just as they may be in any similar outcrop.
Return to the Moss Vale road. A short distance towards Fitzroy Falls, a track on the left leads to the cliff top overlooking Yarrunga Creek.
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| Looking down Yarrunga Ck from Fitzroy Falls June 1972 |
Stop 6. The creek lies 1,400 feet below this point and the slope beneath is composed of all the rock types seen earlier on this excursion. It is a good place to stop and consider the impermanence of our scenery. How long will it take before this valley enlarges to the size of the one we have just left, and how long will it be before all of this is reduced to a plain? When we consider these questions it becomes clear that nature’s own land-shaping forces are on a much grander scale than man’s.
The Moss Vale road joins the Robertson road 1 mile further on, where Excursion 2c continues the narrative at Fitzroy Falls.
Excursion 5b
Broger’s Creek (9 miles)
This is a delightful little valley similar to Kangaroo Valley, but on a smaller scale. Except in its lowest part, near the Kangaroo River junction, the rocks seen along the creek are tuffs of the Gerringong Volcanics. There is little of unusual geological interest, but the scenery is sufficient to make this excursion a must.
Route: Moss Vale road-Broger’s Creek-Wattamolla-Woodhill, thence via Excursion 4a to Berry.
Turn right from the Moss Vale road at the ‘Berry’ signpost, 3.7 miles from the crest of the Cambewarra Range. Stop at Sawyer Creek, a short distance towards Berry.
Stop 1. The gravel of this creek contains the typical rock types derived from the Cambewarra Range. Quartz minerals are not common in this creek or any other tributary of Broger’s Creek. It seems as if their major source area lies between Kangaroo Mountain and Brown’s Mountain, since beyond these limits even jasper is scarcely to be found.
Just beyond the bridge, a road branches to the left, leading to Kangaroo River (2 miles).
One mile further on towards Berry, the road forks. The right branch climbs up the range and over to Berry via Bellawongarah, passing up through the Broughton Sandstone and the Cambewarra Flow before reaching the Coal Measures along the crest of the range. See Excursion 4b.
The left branch closely follows Broger’s Creek for several miles, passing through tuffaceous units of the Berry Formation as far as Wattamolla. This little village, with its old church, cemetery, school and post office no longer in use, is typical of the small community centres of the nineteenth century and it is sad to see history being lost as these centres decay.
Beyond Wattamolla, the road ascends to Woodhill, skirting the back of Broughton Head (Berry Mountain) before joining Excursion 4a at Woodhill Gap.
Questions
1. Give evidence to support the statement that Kangaroo Valley was carved by the normal agents of erosion. 2. Discuss the probable nature of the rocks exposed by drilling at Hampden Bridge to a depth of 1,000 feet. 3. Compare specimens of the Budgong Sandstone (or its equivalent) as seen at various points in Kangaroo Valley. 4. Suppose that Kangaroo Valley is to be turned into a storage reservoir for the Sydney water supply. List arguments against this proposal from the point of view of scenery preservation.
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| Meryla from Cranky Creek Falls December 1975 |
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