Geology Reference
In-Depth Information
(b)
Figure 6.1. (b) The Groot Spitzkoppe, central Namibia.
(a)
Figure 6.2. Bald bornhardts and inselber gs (a) Mt. Lindsa y, Mann Range, central Australia (Mines and
Energy, South Australia).
sidewalls render them unusual and eye-catching. It is because of the perceived dramatic quality of
the residual hills that the inselbergs, and not the more extensive plains, have given their name to
inselberg landscapes or Inselberglandschaften (Figs 1.2e, 1.3a and b
,
and
6.1b).
Inselbergs are characterised by steep bounding slopes which meet the adjacent plains in a sharp,
almost angular, junction, known as the piedmont angle or nick. Inselbergs are of many shapes and
sizes, but the granitic forms are of three major types. By far the most common and widely distrib-
uted is the bornhardt (Twidale, 1980; Twidale and Bourne, 1978), the domical form named after
the German geologist Wilhelm Bornhardt (1900) who, late last centur y, explored parts of East
Africa, and provided some of the most evocative descriptions and beautiful sketches of the forms
and the landscape of which they are part, as well as astute analyses of their possible origins.
Bornhardts are bald, steep-sided domes (Birot, 1958) (Figs 2.1c and 6.2). The flanks of some
gneissic forms display ribs or parallel clefts
(Figs 6.3a and b)
,
but the domical form is everywhere