REPORT OF COMMISSION VII 
GVII-27 
strument for use with aerial photographie prints, that permits determination of 
slope angles in stereoscopic models; (3) experimentation with a tilting platen 
for use with Multiplex-type instruments for determining slope angles in stereo 
scopic models, and (4) experimentation with constructed stereoscopic models for 
training purposes. The results of this latter work are described in “Construction 
of Controlled Stereoscopic Models” by R. J. Hackman. 
Some particularly interesting experimentation has been conducted at the 
U. S. Geological Survey in the use of high altitude photography (1:60,000 scale) 
for geologic mapping. By the use of a Kelsh-type plotter, the stereo-model is 
enlarged approximately five times from the original scale of the photography. 
This technique permits relatively large areas to be studied from the same stereo 
scopic model, as contrasted with the limited area of the usual 1:20,000 scale 
photography. This permits the interpreter to recognize geologic relationships in 
the single model which with large-scale, smaller area photography might be 
discovered only after prolonged study. Further advantages of the technique are 
that excellent plotting accuracies are realized due to the use of a high order 
stereo instrument, and that greater speed and economy in map compilation is 
obtained since a fewer number of stereoscopic models are required per unit area. 
SOME ADDITIONAL PRODUCTION AND RESEARCH PROJECTS 
In the interests of brevity, the following additional photogeologic projects 
active during this period are listed in outline form below: 
Title: General geologic mapping, Colorado Plateau, U.S.A. (production) 
General description: 1:24,000 scale mapping of distribution of sedimentary 
rocks in Colorado Plateau. Mapping all structure, such as folds, faults, and 
joints 
Dates: Begun—1952. This is a continuing project 
Types and scales of Photography: Primarily 1:20,000-scale, vertical 6"—8f"; 
and 1:60,000-scale, vertical 6" photography. All photography is black and 
white 
PI instruments used: Stereoscopes, stereometers, Kail plotter, Kelsh plotter, 
and Multiplex 
Types of information furnished: Structure and distribution of mineralized 
formations, largely Mesozoic in age 
Title: Reconnaissance mapping, Alaska 
General description: Photogeologic mapping in connection with field-photo 
compilations of Alaskan 1:250,000-scale quadrangles. Photo work to show 
geologic information interpretable from photos and commensurate with 
plotting at above scale 
Dates: Begun—1954. This is a continuing project 
Area: 54,000 square miles 
Types and scale of photography: Primarily 1:40,000-scale, vertical, 6" photog 
raphy. Black and white 
PI instruments used: Stereoscopes, stereometers 
Types of information furnished: Generalized structural and stratigraphic in 
formation 
Title: Uinta Basin, Utah, U. S. A. (production) 
General description: Detailed mapping of Green River and Uinta formations 
Dates: August—1952 to March—1954 
Area: 1,200 square miles