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