exploration in recent years has been becoming more and more centred on the 
discovery of subsurface structures, because of the fact that most of the easily 
detectable features have already been explored. Indirect evidence, such as 
vegetation, drainage pattern, etc., is consequently gaining in importance. The 
lithological interpretation is especially important in the search for ore deposits. 
Geomorphology plays an important role in this respect, and also in the study 
of alluvial (placer) deposits. The hydrogeologist will concentrate on the esti 
mation of surface run-off and infiltration, because the permeability/porosity 
of the rock is an indication of its value as an aquifer. Possible water reservoirs 
can thus be located on the strength of structural geomorphological and vegeta- 
tional evidence. The engineering geologist will concentrate on the surface 
materials and their engineering properties, such as drainage, bearing strength, 
compressibility, etc. 
Although each of the above mentioned types of photogeological studies has 
its own aim and its own characteristics, all of them are most valuable contri 
butions to the inventory of natural resources, and especially for the develop 
ment of mining and industry, which is a prerequisite for the raising of the 
standard of living above the subsistence level. 
Development of agriculture, of course, is also a need for every country. Only 
a small part of this development can be arrived at by introducing some 
improvements into the existing system of subsistence farming. In many cases 
subsistence farming, even in the least densely populated countries, is doing its 
utmost by producing all the food and some raw materials which can be prod 
uced under the prevailing technical and economic circumstances. In many 
cases even more than that has been done, and this has resulted in very serious 
erosion damage and in the breaking down of the age-old cycles of shifting 
cultivation. Of course, the talk is always about the opening up of new lands, 
which are still under “virgin forest”. But the surface area of these is extremely 
small, and even then it is found that, in most parts of Asia and Africa, only 
those areas are still virgin forest which are not suitable for subsistence farming 
and which are sometimes not even suitable for any farming whatsoever. Only 
some parts of tropical America may be more promising in this respect. 
A different aspect is seen in considering the reclamation of virgin alluvial 
lands, whether forested or not. Here, certainly, we find areas in many parts of 
the world which can be made suitable for the agricultural production of food 
and of some raw materials for industry. But in general this can only be done 
with considerable investment, because dams and dikes must be built, drainage 
and sometimes irrigation systems must be constructed and various other in 
stitutional and technical means must be provided. 
We may, therefore, conclude, that the development of subsistence farming as 
such will never give a lasting solution to the problems of development of agri 
culture. This means that the traditional systems of agriculture must be mod 
ified, and sometimes even totally changed, by bringing into use the technical 
inventions of the modern world, such as insecticides, fungicides, chemical