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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962
Fig. 4.
Differential weathering in arid areas
Intrusive granite (Gfi preferentially reduced in schists (X) and partially granitised rock (GX).
Note resistant autochthonous granite (G)
Beihan area, Aden Protectorate
R.A.F. Photograph. Crown Copyright Reserved
the limestone is the dominant rock, and in contrast with the latter, quartzite
often displays a less rugged and more rounded form. Although under arid
conditions chemical reduction of limestone - by solution - is minimal, quartzite
is yet more chemically resistant. The topographical dominance of the lime
stone is due to its greater resistance to thermal disintegration. The extreme
resistance to total weathering of both these rock types is a valuable guide to
identification.
Clearly demonstrated on aerial photographs is the high degree of reduction
suffered by intrusive granite. In numerous instances in Aden and Somaliland
granite areas are marked by plain-like arenas studded with inselbergs and
exfoliated kopjes. The Las Bar granite of Somaliland is surrounded by an
