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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
lelism of long ridges of quartzo-feldspathic gneiss with the foliation of the 
adjacent biotite gneiss in an area of complex isoclinal folds. 
It is not claimed that bedding and foliation coincide under all conditions of 
regional metamorphism. It seems probable that original bedding will be 
observed on air photographs as metasedimentary foliation only when the 
recrystallisation of the original sediments had taken place under relatively 
static conditions of confining pressure. If the recrystallisation of the sediments 
had taken place under conditions of strong directed stress, the foliation of the 
banded gneisses might well be in a direction and plane different from that of 
the sedimentary bedding. The rocks in the Mahenge area, for instance, have 
undergone at least two periods of folding and yet there is good evidence that 
bedding and foliation coincide even round the nose of the main syncline. This 
suggests that recrystallisation in this area took place under fairly static condi 
tions. If the recrystallisation and folding of the rocks had taken place under 
strong directed stress the metasedimentary foliation would have developed 
parallel to the axial plane of the folds. 
It would appear, therefore, that airphotographs may contain evidence of 
the conditions of regional metamorphism, and indicate whether recrystallisa 
tion took place under confining pressure or directed stress. 
Conclusions 
The application of reconnaissance photogeology to mineral exploration in 
areas of regional metamorphism is necessarily limited. Systematic prospecting 
requires detailed work by field geologists, but photogeology can sometimes 
indicate those areas most suitable for prospecting, for instance when mineralised 
rock occurs in outcrops large enough for photogeological interpretation or 
when it is associated with recognisable dykes, other minor intrusions, or 
fracture zones. Photogeology can also provide a basis for prospecting when 
the mineralisation is related to original sedimentary bedding as is the case 
with graphite and, in certain circumstances, pyrite. Then it is necessary to 
know whether the metasedimentary foliation represents original bedding, and 
for this also, the air photographs can often provide the clue. 
Discussion 
R. Mühlfeld: The examples presented show parallelism between bedding and foliation. How 
would a case where such parallelism does not exist present itself? Answer: If there is a fold with 
axial plane foliation one must expect the ridges representing the bedding to be more pro 
nounced along the arms of the fold where the foliation is more closely parallel to the bedding 
than in the nose of the fold, where the foliation makes a large angle with the bedding. This 
answer, however, contains a large measure of speculation and requires considerable quali 
fication.