Geology Reference
In-Depth Information
(a)
(b)
Figure 3.6.
(a) Photograph (b) sketch of 2 m thick regolith exposed in quarry at Yarwondutta Rock, near
Minnipa, northwestern Eyre Peninsula, South Australia. A - soil; B - Grus with limestone nodules;
C - laminated granite; D - FeO-rich zone; E - Fresh granite.
rock increases dramatically, so that more water penetrates and more alteration rapidly occurs. The
weathering front descends from the surface to depths of a few metres (Fig. 3.6), or, in humid trop-
ical lands, several scores, or even a few hundreds, of metres (Branner, 1896). Thus, in many places
the continents carry a skin of regolithic material which is important not only by virtue of the sur-
face soil, but also because it holds water. Reactions between regolithic moisture and the underly-
ing bedrock are responsible for many familiar landforms both in granitic terrains and elsewhere.
Because the regolith develops from above and penetrates down (and laterally) into the country
rock, the initial phase or stage of weathering is found at the weathering front and successively
higher zones indicating stages of more advanced weathering. At many sites, both in granite and in
