488 
SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
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 
Base 
8 
100 
15 
Sub-base 
18 
35 
30 
Quantity 
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 
complete). 
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.