Sftf SSSmSKBS. ■ ISSÏÏv - ,
WORKING GROUP 9
ATKINSON-BROWN
491
It occurs alone or in association with other trees, but its ease of identification
on 1 : 20,000 airphotos is not known.
The laterites are of several types sometimes being closely associated with
quartz gravels. Thus, the useful deposits range from quartz gravels through
laterised quartz gravel to quartz laterite, laterite gravel and laterite with no
quartz. Some of the softer laterites are usable, but generally the lateritie clays
developed over the dolerites are of no value as construction materials. A
stripping ratio of 1 : 1 for overburden laterite is used in conjunction with haulage
distance and availability of other materials to determine the economics of
excavation. Overburden is blade-bulldozed off and stockpiled for subsequent
infilling, the laterite or gravel is loosened by ripping and the extraction is by
means of a bulldozer.
It is considered that, using the criteria described and demonstrated on the
photographs, a good degree of success in the location of deposits has been
attained and that by extending these methods in similar areas, better results
could well be achieved.
Ackno wledgem ent
Grateful acknowledgement is made to Mr. J. H. Durr, C.B.E., Commission
er of Roads and Road Traffic, S. Rhodesian Government and to the Directors
of Hunting Technical Services Limited for permission to publish this paper;
to Dr. F. J. Amm, Chief Mining Engineer, Mines Department S. Rhodesian
Government for geological information and to the Road Research Laboratory,
D.S.I.R. England for helpful discussions and criticisms.
References
1. Brown, N. B. Notes on the Location of Liatertic Road Materials. Unpubl. report to
Central Road Lab., S. Rhodesia.
2. Milne, G. Some Suggested Units of Classification and Mapping Particularly for E. Afri
can Soils. Soil Res. 4: 183-198. 1935.
Milne, G. Composite units for the Mapping of Complex Soil Associations. Trans 3rd Int.
Congr. Soil Sci. Oxford. I 345-347. 1935.
3. Precott, J. and Pendleton, R. Laterite and Lateritie Soils. Commonwealth Bureau of
Soil Sci. Techn. Comm. 47. 1952.
4. Mohr, E. and van Baren, F. Tropical Soils. Chaps XII and XVI, 1954.
5. Amm, F. J. Unpubl. geological map and field notes. Sheet 1731 Do. Geological Survey
Dept., S. Rhodesia, 1953.
