Magnificent sandstone formations

Five main rock strata dominate the Golden Gate Highlands National Park in South Africa. The top layer consists of hard Drakensberg basalt, the cooled lava from ancient volcanic eruptions about 183 million years old.

The next, rather thin layer, originally sandstone, was metamorphosed by the hot lava to form hard quartzite. The thickest and most colourful strata are Clarens Sandstone, ancient sands laid down over a dry period some 190 to 196 million years ago.

This soft rock erodes easily where it is not protected by the basalt and quartzite capping. In many places, a narrow, harder, calcified stratum has formed within the Clarens layer, a result of waterborne calcium carbonate combining with the sandstone.

The lowest stratum is the Elliot Mudstone, laid down as thick layers of silt and mud around 200 million BP when the area was a wetland, then dried and compressed to rock by pressure from above. Black vertical stripes on the sandstone are manganese dioxide, leached from the basalt by water seepage.

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