Geology Reference
In-Depth Information
(c)
(d)
Figure 6.19. (c) The Vredefort brick pit in 1979, showing part of a granite dome (X) exposed in a corner of
the quar ry. (d) Granite dome e xposed b y roadw orks at Midrand , betw een Pretoria and
Johannesburg, South Africa.
Yarwondutta Rock pro vides a clear , compact e xample (
Figs 6.21a
and b). F ormer hill-plain
junctions are indicated by the upper shoulders of the two flared slopes preserved on the northern
side of the Rock. Bearing in mind the origin of flared slopes, it is deduced that:
-Yarwondutta Rock has emerged and grown as a positive relief feature as a result of the episodic
or phased lowering, by streams, of the surrounding plains.
- This emergence has taken place not g radually but in distinct phases or episodes. The flared
weathering fronts imply comparative standstill, time during w hich scarp-foot weathering has
taken place. Their exposure, on the other hand , indicates stream rejuv enation and landscape
revival, during which the plains w ere lowered, but the residuals remained in relief. Whether
the scar p-foot zone w as etched out deeper and deeper in successive stages of de velopment
(
Fig. 6.22a)
,
or whether there were successive lowerings of the plains (Fig. 6.22b) is not known.
