Kirstenbosch Geological Sites Page 2

[9] Stronger creeks such as Skeleton Gorge continually sweep away the sandstone talus, revealing the softer more massive Cape granite

[10] The lower forested slopes of Kirstenbosch are underlain by Cape granite, but which seldom outcrops due the voluminous talus cover derived from the sandstone cliffs, but some creeks have washed away this veneer and expose the bedrock

[10] A fresh sample of Cape granite has a distinctive texture containing large white crystals of Orthoclase feldspar surrounded by smaller grains of milky white Plagioclase Feldspar, grey Quartz and black Biotite

[10] Outcrops of Cape granite in the Rooikat Ravine at Kirstenbosch always show signs of weathering

Weathering of the Cape granite develops gradually with the plagioclase feldspar decomposing to clay, liberating the other minerals like quartz and the bigger crystals of orthoclase feldspar

Breakdown of the weathered granite often causes a crude pillar structure when a harder, more resistant crystal of orthoclase feldspar or quartz caps a small tower of clay-rich sand (field of view = 10cm)

[11] Grey sandstones of the Peninsula Formation form the high cliffs that rise above Kirstenbosch. Heavy rains cause slope failure and landslips scar the lower forested slopes

[12] The weathered talus that collects on shallow slopes develop a thin soil that supports vegetation, but often fails after heavy rain

[13] Cliffs of Table Mountain sandstone erode mainly by overhang collapse and wedge failure, due to the horizontally bedded nature and numerous vertical joints

[14] Balancing boulders mark the temporary resting place of blocks dislodged from the sandstone cliffs

[15] Cliff failure can result in the detachment of extremely large tabular blocks of Table Mountain sandstone that tumble down the slopes, like these at the north entrance to Kirstenbosch on the contour path

[16] Slope failure in the thinly bedded Graafwater Formation strata usually collect in the beds of streams draining the steep cliffs, such as Vaalkatkloof


[8] Contact between the Graafwater Formation and the Cape Granite. Vaalkatkloof Stream at its junction with Nursery Stream.	[8] Contact between the Graafwater Formation and the Cape Granite. Vaalkatkloof Stream at its junction with Nursery Stream.	[9] Granite outcrops form the waterfall in Skeleton Gorge at the point where it is crossed by the Contour Path	[9] In the winter the Skeleton Gorge stream flows over the granite falls

[9] Stronger creeks such as Skeleton Gorge continually sweep away the sandstone talus, revealing the softer more massive Cape granite	[10] The lower forested slopes of Kirstenbosch are underlain by Cape granite, but which seldom outcrops due the voluminous talus cover derived from the sandstone cliffs, but some creeks have washed away this veneer and expose the bedrock	[10] A fresh sample of Cape granite has a distinctive texture containing large white crystals of Orthoclase feldspar surrounded by smaller grains of milky white Plagioclase Feldspar, grey Quartz and black Biotite	[10] Outcrops of Cape granite in the Rooikat Ravine at Kirstenbosch always show signs of weathering

Weathering of the Cape granite develops gradually with the plagioclase feldspar decomposing to clay, liberating the other minerals like quartz and the bigger crystals of orthoclase feldspar	Breakdown of the weathered granite often causes a crude pillar structure when a harder, more resistant crystal of orthoclase feldspar or quartz caps a small tower of clay-rich sand (field of view = 10cm)	[11] Grey sandstones of the Peninsula Formation form the high cliffs that rise above Kirstenbosch. Heavy rains cause slope failure and landslips scar the lower forested slopes	[12] The weathered talus that collects on shallow slopes develop a thin soil that supports vegetation, but often fails after heavy rain

[13] Cliffs of Table Mountain sandstone erode mainly by overhang collapse and wedge failure, due to the horizontally bedded nature and numerous vertical joints	[14] Balancing boulders mark the temporary resting place of blocks dislodged from the sandstone cliffs	[15] Cliff failure can result in the detachment of extremely large tabular blocks of Table Mountain sandstone that tumble down the slopes, like these at the north entrance to Kirstenbosch on the contour path	[16] Slope failure in the thinly bedded Graafwater Formation strata usually collect in the beds of streams draining the steep cliffs, such as Vaalkatkloof