REPORT OF COMMISSION VII 
GVII-23 
partments. Photographic coverage in these territories is not yet complete but is 
nevertheless available for very large areas. The photographs, taken at a com 
promise scale are verticals of about 1:30,000, taken with a 6" lens, and although 
not always ideal, are generally well suited to photogeological work. Early in 1949 
a photogeological section was set up in the Directorate of Colonial Geological 
Surveys in London to handle specialist problems in this field for the individual 
territories. This section at present has a staff of four full-time geologists who, as 
the need arises, may also make visits abroad for the purpose of following up or 
checking in the field the results of their work. This does not mean that Colonial 
photogeological work has been centralized, but the section is able to act as a 
clearing house for this type of work, to make sure that its value and use are not 
overlooked, and to spend a certain amount of time on work of a research char 
acter. 
It is well known that the most extensive and, so far, probably the most re 
warding geological work on aerial photographs has been done in areas of sedi 
mentary rocks. Large areas of the British Colonial Territories are occupied by the 
ancient metamorphic and igneous rocks, so that a good deal of attention has been 
paid to the question of getting results of geological value from areas of this type, 
particularly in Africa. Interesting results, to name one instance, have been ob 
tained in the study of ring structures. 
Apart from day-to-day use of photographs by geologists in the field, the 
headquarters section has included in its work the making of photogeological 
maps of selected areas of Karroo rocks in Northern Rhodesia and Nyasaland (a 
detailed structural study of a coal-bearing area being made in the latter coun 
try), initial reconnaissance maps followed by field visits in the British Terri 
tories in Borneo, and studies of areas of ancient rocks in Somaliland and Nigeria. 
Photogeological methods are sometimes of particular value and interest in 
connection with special problems, and a small case in point is provided by the 
geological examination of a proposed dam site in Malaya. A description of this 
will shortly be published in Vol. V, No. 4 of Colonial Geology and Mineral Re 
sources entitled “Investigations upon a Proposed Dam Site at Klang Gates, 
F.M.S.” by J. B. Alexander and W. J. Procter. 
The photogeological section also gives a three and a half weeks course annu 
ally to all geologists newly appointed to Colonial Geological Survey Depart 
ments, to acquaint them with the techniques and range of photogeological work. 
As the actual interpretation in photogeological work is largely qualitative, 
no instruments other than a good mirror stereoscope are normally used, but for 
special problems and for the transfer of work to maps, use is of course made of 
standard photogrammetric techniques. It is however of paramount importance 
that the stereoscope be mounted on a good parallel guidance mechanism; 
through its interest the photogeological section was partly responsible for the 
appearance on the market in the United Kingdom, of a satisfactory parallel 
guidance mechanism. 
British commercial air survey companies have also shown very considerable 
interest in geological investigations and to this end employ geologists, either as 
consultants or on their own staff. Here too there has been a recent tendency to 
study areas of ancient metamorphic and igneous rocks as well as more recent 
sedimentarles. Hunting Aerosurveys is currently carrying out, solely by means 
of photographic interpretation, an initial geological mapping project in part of 
Mauretania where existing geological maps comprise only a reconnaissance 
sheet. The same company recently completed a map at a scale of 1:50,000 of 
structural trends in the pre-Cambrian in the Tekhammalt region of the Hoggar.