Geology Reference
In-Depth Information
(b)
(c)
Figure 5.21.
(b) On a bornhardt near Garies, Namaqualand, Western Cape Province South Africa; (c) on
Little Wudinna Hill, northwestern Eyre Peninsula, South Australia.
5.9
SUMMARY
Though granite boulders are formed in several ways, most are due to a combination of two
processes involving, first, differential fracture-controlled subsurface moisture weathering which
produces corestones set in a matrix of grus, and then erosion, most commonly by wash and
streams, which evacuates the grus and exposes the corestones as boulders. Such a two-stage
development clearly applies to granite boulders in many parts of the world, and has operated under
