The final phase of photogeologic training is a review of 
certain photogeologic problems and the resulting geologic maps 
that have been compiled with photogrammetric equipment, Such 
projects have been undertaken by a group of Survey geologists 
who specialize more or less exclusively in making geologic in- 
terpretations from aerial photographs,  Photogeologic mapping 
projects include a series of photogeologic quadrangle maps of 
the Colorado Plateau and Alaska, an isopachous study using a 
Kelsh plotter to compute the thickness of the stratigraphic 
units, and photogeologic mapping with a Kelsh plotter using so- 
called high-altitude photographs at scales ranging from 1:60,000 
to 1:70,000. Also included in the training program are exhibits 
of special types of aerial photographs, such as infra red and 
aerial ecktachrome vertical photographs and low-altitude 9 by 
18-inch oblique photographs. Geologists not familiar with these 
special types of aerial photographs may evaluate the use of such 
photography in particular geologic problems. 
As has been shown in the foregoing discussion photogeologic 
training in the U. S. Geological Survey 1s aimed at providing 
the geologist with a working knowledge of photogeologic-photo- 
grammetric techniques that have proven useful in geologic studies, 
Emphasis is placed on the understanding of the various instru- 
ments and their relative merits and application to particular 
geologic problems,