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Transactions of the Symposium on Photo Interpretation

Wendung zu finden, während diejenigen granitischer Gesteine, d.h. Latent oder quarzreiche
lateritische Schotter, den Anforderungen entsprechen.
In dieser vorläufigen Studie wurde ein hoher Genauigkeitsgrad in der Höfflichkeit möglicher
lateritischer Bildungen erreicht.
This study results from an initial research by N. B. Brown undertaken for the
Central Road Laboratory, S. Rhodesia, into the feasibility of utilizing airphoto
interpretation to locate lateritie road construction materials along a route in
the Macheke District. It was followed by interpretation and field checking by
J. R. Atkinson in S. Rhodesia, subsequent interpretation and analysis being
done jointly.
The area is situated 10 miles north of Macheke extending 10 miles further
northward. The route is covered by airphotos at 1 : 20,000 scale. The require
ments of the Division of Roads and Road Traffic for latente deposits used for
road construction are shown in table 1.
Table 1. Specification for Lateritie Road Materials
C.B.R. m i n
Max. % passing 200 BS sieve
7,000 cubic yards per mile per
12 inch thickness of base and sub-base.
Note: Where the plasticity index is too high, 2-3% lime can be added to decrease it and to
increase the strength of the material.
This specification shows that zones of clay soils are unlikely to provide satis
factory material and that large quantities of laterite are required. Selection of
potentially lateritie areas was based on airphoto interpretation from the main
aspects of geology, geomorphology and pedology. Some of the original criteria
[1] for the recognition of such areas are as follows:
a. The presence of suitable parent material.
b. The preservation of suitable landforms.
c. Recognition of the position in a catenary soil sequence (complete or in
These criteria derive principally from the concepts of Milne [2], Prescott
& Pendleton [3], and Mohr [4], and have been amplified in detail and aug
mented by field checking and airphoto interpretation.
The close association in Central Africa of parent rock materials and the
generally sedentary soils makes it difficult to separate the aspects of geological
and pedological photo interpretation. In areas of virgin bush there is little
evidence of soil erosion except around the incised vleis. However, where farm
ing has disturbed the natural regime, soil transport is quite marked in many
places and the photo-tones and textures of the soils may be modified. In gen
eral, a good interpolation of geological boundaries can be made utilizing dif
ferences in soil colours.