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The Scenery and Geology of The Wilderness Area
By Paul Rixom
The scenery and geology of the Wilderness area are closely interlinked. But before we look at the
rocks that give rise to the local landscape we must first get a basic understanding of the three main
rock types that occur on earth, which are all present in the Wilderness area. The three main types
are igneous, sedimentary and metamorphic rocks. The diagram below illustrates ‘The Rock Cycle’
The Rock Cycle
Tectonics (uplift)
Igneous rock
Intrusion
into Crust
Weathering and
Erosion
Transportation,
Deposition and
Lithification
Magma
Partial melting
Partial melting
of mantle material
Ultra
Metamorphism
Sedimentary Rock
Contact & Regional
Metamorphism
Metamorphic Rocks
As the earth started to consolidate 4.5 billion years ago molten rock, called magma, rose up from the
earth’s mantle into the crust and solidified into what we call igneous rock (latin - ignis – fire). Those
first igneous rocks were uplifted by tectonic forces into mountains and then weathered by rain and
wind into small particles which were carried down mainly by rivers into oceans and lakes and
deposited as sediment on the bed of those aquatic bodies. Over time these particles hardened, or
lithified, into sedimentary rocks. These sedimentary rocks can now be uplifted by tectonic forces into
mountains which can be weathered again. If we now take those sedimentary rocks, and also some of
the igneous rocks, and bury them deep in the earth’s crust and subject them to heat and pressure
they will change them into metamorphic rocks (metamorphosis – change) which will in due course
be uplifted again to form mountains and subsequently eroded. Ultimately, heating and burying these
rocks will melt them back to magma and the ‘Rock Cycle’ has then turned full circle. This cycle has
been in operation since the creation of the earth 4.5 billion years ago.
As mentioned above the Wilderness area contains examples of all these three rock types which give
rise to the local scenery and land forms.
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The Three Main Types of Rocks in the Wilderness Area
Metamorphic rock –
Phyllite
Igneous rock –
Cape Granite
Kaaimans Formation
Touw Waterfall
Serpentine Road
Dolphin Point
Cape Granite
Touw Waterfall
Wilderness
Sedimentary rock –
Table Mountain Sandstone
Cape Supergroup
Table Mountain Sandstone
Outeniqua Mountains
Igneous Rocks – Cape Granite – About 600 million yeas old.
This rock can be seen on a road cutting to the left just before the Wilderness turn off coming in on
the N2 from George. But the best place to see the Cape Granite in the Wilderness area is at the
Touw waterfall at the end of the National Parks trail. Large rounded boulders of Cape granite have
provided the hard rock that has actually formed the waterfall. The rock is quite massive with no
apparent bedding. If you look closely at the rock you can seen fairly large grains of quartz (white),
feldspar (grey) and mica (black) that have crystallised out as the originally molten magma cooled
down.
Cape granite at the Touw waterfall
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Metamorphic Rocks – Kaaimans Phyllite – About 650 million years old.
When walking along the specially constructed wooden walkway in the National Park just before you
get to the Touw waterfall you walk underneath a finely laminated, well bedded, steeply dipping rock
which is the Kaaimans phyllite metamorphic rock. This rock was originally deposited as a muddy
shale in an ancient sea about 650 million years ago but became the metamorphic rock called phyllite
(greek – phyllon – leaf) due to the pressure of tectonic forces and to some extent the heat of the
intrusion of the adjacent Cape Granite. In fact in the Wilderness area the two rock types of the
Kaaimans phyllite and the Cape granite are closely interwoven in a very complex way. For it is only a
couple of hundred metres further along the walkway that you encounter the very different rock
represented by the intrusion of the Cape granite at the waterfall.
Kaaimans phyllites below the Touw waterfall
Another place to see the Kaaimans phyllites is in the road cuttings along the Serpentine Road going
up to Hoekwil. Again, steeply dipping laminations point down toward the road and in times of very
heavy rain rock falls have be known to occur. Wilderness Heights and Hoekwil are situated on a river
dissected plateau at about 200 metres above sea level and the Kaaimans phyllites underlie the
villages and some of the dairying farming land to the east.
Kaaimans phyllites above the Serpentine road
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The collapse of the N2 at Dolphin Point during the floods of 2006 was due to the heavy rain getting
inside the fine laminations of the Kaaimans phyllite which in that area dip steeply towards the sea.
This caused the rock to slip down along the laminations which moved the concrete support columns
of the road opening up a very large and long crack in the vicinity of Dolphin Point. Apparently when
the road was widened and built out on concrete columns in the 1980’s geologists warned of
‘unfavourable geological conditions’. The lengthy piling and reconstruction work appears to have
held up during subsequent heavy rains.
Sedimentary Rocks – Table Mountain Sandstone – About 500 million years old
The Outeniqua Mountains above Wilderness Heights and Hoekwil are made of Table Mountain
Sandstone. One of the best places to view the Outeniqua Mountains is just north of the village of
Hoekwil before Touwsranten. Look to the left over the Strydom Farm to George and Cradock Peak
above George. You can see quite clearly that the Table Mountain Sandstone is dipping about 30o to
the south (to your left). Now remember that these sedimentary rocks were laid down in a sea, in this
case the ancient Agulhas Sea, about 500 million years ago. But at about 330 million years ago great
compressional tectonic forces came from the south and folded and uplifted these hard consolidated
rocks into the Outeniqua, Kammanassie and Swartberg Mountains. The forces were so great that the
Table Mountain sandstone of George and Cradock peak is actually overturned or upside down. In
other words it started as strong, hard horizontal bedded rocks but were pushed (like a loose carpet
on a tiled floor) up to the vertical position and then over the vertical by another 60o so that they now
are inverted and dipping 30o to the south.
George and Cradock peaks. Overturned Table Mountain sandstone, dipping about 30o to the South
Dip 30o to
the South
It is important to remember that at the time of the uplift and folding the Outeniqua Mountains were
probably about 5000 metres high. Now, two-thirds of their height has been removed by erosion.
Another place near Hoekwil to view the Table Mountain Sandstone of the Outeniqua Mountains is
the road that goes up to the Bergplaas Cape Pine plantations. This road is a left turn off the Seven
Passes Road past the Woodville Big Tree and climbs up over Table Mountain sandstone into the
Cape Pine settlement situated in a massive bowl in the mountains carved out by the Dieprivier. Good
views are also obtained looking south over the agricultural plateau.
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Wave Cut Platforms
As mentioned previously Wilderness Heights and Hoekwil are situated on a river dissected plateau at
about 200 metres above sea level. This plateau is evident all along the Southern Cape coast and
Garden Route. At Wilderness Heights the plateau is only about 5 km wide south-north to the base of
the Outeniqua Mountains, but going west towards and beyond Mossel Bay it is over 30km wide. The
geologists refer to this plateau as a wave-cut platform, which means it has been created by sea
action when the sea was 200 metres higher than it is now.
Wave Cut Platform – Agricultural land looking South from the Bergplaas road – Ancient sand dune
cordon in the distance – Swartvlei to the left.
Sea level changes over the last approximately 80 million years
High Sea Level Shoreline approx. 200 m above current sea level
Wilderness
Low Sea Level Shoreline approx. 180 m below current sea level
The above diagram shows the high and low level coastlines over the last approximately 80 million
years along the Garden Route. The low levels reflect a glacial period when the earth’s ice caps were
at their greatest extent and much water was held as ice and the high levels reflect an inter-glacial
period when most of the ice caps had melted. The cave above the seven passes road on the Strydom
Farm is possibly a sea cave eroded out of a fossil cliff when the sea was 200 metres higher than now.
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Possible sea cave and sea cliff – Strydom Farm – From the Seven Passes Road
Changes in sea levels – Wave cut platforms and fossil cliffs
Wilderness
Heights
Coastal wave-cut platform:
Av gradient - 1:300 seaward,
Width – 2 km to 30 km
The above three diagrams show how the wave-cut platform on which Wilderness Heights is now
situated has been formed as a result of very high and very low sea levels. Also uplift of this southern
part of Africa around 20 and 5 million years ago has caused the rivers like the Touw and the
Kaaimans to cut very deep, steep sided gorges.
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Global sea level changes over the last 140 million years.
Geologically Recent Sand Dunes
When we look down from the Serpentine Road, below Hoekwil, onto the lakes area we see the
distant Rondevlei and Langvlei off to the east and the much closer Eilandvlei linked by the
Serpentine Channel to the Touw River at Ebb and Flow which finally escapes to the sea, when the
mouth is open, at Wilderness. The rivers such as the Duiwe and the Touw, and some smaller rivers to
the east used to flow directly into the sea, but a ‘cordon’ of sand dunes was formed which blocked
them from the sea, formed inland lakes and finally diverted the rivers west to escape at Wilderness.
Eilandvlei, Langvlei and Rondevlei formed by rivers blocked from the sea by sand dunes
These sand dunes, upon which Wilderness East and other areas are situated, are probably less than
2 million years old, which is very young in geological time. They were formed during glacial periods
when the sea level fell and receded many kilometres away, forming almost a desert in which windblown sand formed large sand dunes blocking the rivers from the sea. There are also some fossil
drowned dunes off the Wilderness to Sedgefield coast.
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Wilderness East built on a fossil sand dune cordon forcing the Serpentine Channel to join the Touw
River before it can exit to the sea.
Thousands of years ago the Touw River used to flow directly to the sea, near the present Fairy
Knowe hotel, but was diverted west by the sand dune over which the N2 now runs. In fact in August
1883 when Krakatoa exploded in the present Indonesia, the young Roderick Dumbleton (10 years
old) remembers the resulting global tsunami actually breaking over the sand dune into the river.
Touw River at Fairy Knowe, circa early 1920s, before the national road. Fairy Knowe hotel
buildings are on the river, and the original house, built in 1874, now the Backpackers, stands on a
small hill.
We hope this little guide will assist you in understanding a little of the underlying geology that has
given rise to the beautiful scenery of the Wilderness and Hoekwil area.