Geology Reference
In-Depth Information
Bornhardts could have been initiated by subsurface structurally-controlled weathering in any cli-
matic context, though the agents responsib le for burial, and for subsequent e xposure, have no
doubt varied from place to place and time to time. Thus, the inselber gs of F ennoscandia and
Galicia-Northern Portugal were initiated in warm humid conditions during the Tertiary but were
exposed by glacial action during the Quaternary, whereas the stripping of tors on Dartmoor, south-
western England, is in part at least due to nival action, and the (phased) exposure of some of the
Eyre Peninsula, South Australia, inselbergs, for instance, can be attributed largely to fluvial action,
(c)
(d)
Figure 6.31. (c) Section sho wing g ranite hills re-e xposed b y the par tial stripping of the co ver of
Carboniferous sandstone (and by the erosion of the grus from the fracture zones?) in the Tassili
Mountains of souther n Algeria (Barbier, 1967). (d) Sk etch showing exhumed subCambrian
granitic hills from the Namibia-Namaqualand (W
estern Cape Pro vince) border district
(Du Toit, 1937).
(a)
Figure 6.32. (a) These granite domes near Port Hedland, in the north of Western Australia, have been covered
by the Early Cretaceous seas and sediments (the latter for ming the plateaux), and then par tly
re-exposed. They are of exhumed type and preCretaceous age.
