GVII-3 (Sup.) 
NATURAL RESOURCES 
Geology 
In Switzerland, geological surveys carried out for pre 
liminary study and advice and for subsequent control of 
engineering projects are making continuous and extensive use 
of photographs. For such technical purposes preference is 
given to the well known working method, developed by the 
late Dr. Rob. Helbling. It is of special value in the 
structurally most complicated and often badly accessible 
alpine regions. The method is based on the principles of 
accurate photogrammetric plotting of both, topography and 
geology, and it is capable of answering the most exacting 
demands. The plotting of the geological evidence at least 
is, by preference, carried out by the geologist who did the 
field work. This, of course, implies that the geologist be 
carefully trained. If this is not the case, he at least 
supervises the geological part of the plotting, which, as 
a whole, can be done by any private surveying office equipped 
for high-accuracy photogrammetric work, 
In the Netherlands during this reporting period, 
photogeological interpretation was mainly carried out for 
instruction and no larger projects were accomplished * 
Forty-five smaller areas of varying size (from two to 
fifty-three photographs) of different parts of the world 
and featuring all kinds of geological phenomena were worked 
out in detail by the International Training Center for 
Aerial Survey (ITC) staff and about thirty areas by students 
of the ITC and of Utrecht University. In some cases geo 
logical section were drawn on an entirely photogeological 
basis. Two photogeological maps were produced in coopera 
tion with the Pedological and Forestry Sections of the ITC 
(Ethiopia and Iraq respectively) as samples of different 
kinds of interpretation of the same area. 
In these Netherlands projects, over £00 photos were 
worked out in detail and many others in reconnaissance 
style. Features dealt with included both simple and 
complicated structural geology (including multiple thrus 
ting, imbrication, close folding, etc,) (Pakistan, New 
Guinea, Algeria, Iraq, Spain, Montana, USA, Switzerland) 
intrusive areas, batholiths, laccoliths, contact-zones, 
metamorphics (Montana, USA), su.brecent volcanic regions 
(Ethiopia, France) glacial geology dealing with the 
shrinking of existing glaciation and with glacial deposits 
(Central Alps, Montana, USA), terrace landscapes with up 
to 10 levels of depositional terraces (Montana, USA) and 
the behavior of streams and rivers alluviation and down 
cutting, slumping, etc. Stratigraphic correlation was