The listed coordinates will take you to the start of the Geological Rock Garden where there are some 20 ultra-large rock specimens from all over the region, which have been brought to the Garden for display. They are laid out in a landscaped area of the Garden in order of geological time, starting with ancient basement granites and greenstones, moving upwards through time to end with specimens from the Karoo, and even younger cave breccia. Take note here as most answers to the questions can be found in this Rock Garden.
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Logging Tasks:
1) Greenstones are among South Africa’s oldest rocks. How were they formed?
2) How were these quartzite rocks formed?
3) How were the whitish patches of veins of the mineral quartz intruded into quartzite rock?
4) After the tillite rock display what rock display is found next at these coordinates S26 05.328 E027 50.571?
Move on to view the cliff of quartzites and shales and the waterfall that is situated at S26 05.520 E027 50.426 to answer question 5.
5) Where do the shale beds become more prominent in the cliff face?
This picture is of a quartzite rock on display in the rock garden.
The rock-face you see to the left of the falls consists of interbedded quartzite (light grey) and shale (reddish brown) of the Orange Grove Formation at the base of the Witwatersrand Supergroup. The quartzites represent sand that was deposited in a shallow sea approximately 2,700 million years ago; ancient wave ripple marks are present on bedding planes in the quartzite. The shales represent muds that settled in the quiet deeper-water environments of the ancient sea. Shale beds become more prominent upwards, indicating that the land became progressively more deeply submerged under the sea with time. The quartzites are resistant to weathering and form the escarpment. A fault displaces the beds along the small gully on the left side of the rock face.
At the start of the Crocodile River, the Witpoortjie Waterfall plunges 70 m over ledges of south-dipping Orange Grove Formation quartzite and shale, which in turn overlies much older greenstone.
There is also the JCI Geological Trail that starts at the base of the waterfall. The trail follows a roughly circular route that takes in major geological features and marker beds of the south-dipping, lowermost formations of the West Rand Group, including the Orange Grove quartzite and Parktown shales, and returns via outcrops of 3,500 million year old talc schist of the underlying greenstone formation.