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through the medium of aerial photography, and 3) development and adaptation 
of film types to geologic problems. 
The relatively recent use of stereoplotting instruments, particularly the Kelsh 
plotter, in conjunction with high-altitude photography is an outstanding example 
of adaptation of photogrammetric instruments to geologic problems. It has been 
demonstrated that not only can satisfactory interpretive results be obtained 
from 1: 60 000-scale photography, but such results can be obtained in less than 
half the time than when the normally employed 1: 20 000-scale photography is 
used. 
Other instruments being evaluated in photogeologic study are the tilting 
platen, for use with multiplex-type stereoscopic models, the profile plotter, also 
for use with multiplex-type stereoscopic models, and the Super-Duper Dipper 
(Stereo-slope Comparator) for determination of dip of planes in stereoscopic 
models from paper prints. 
Vertical color photography of small areas in California and Nevada is being 
evaluated as an adjunct to geologic study. This photography is at a scale of 
1: 10 000 and was taken with a 12-inch focal-length lens. 
Training in photogeology is carried out formally in Menlo Park, California, 
and Denver, Colorado, and informally in Washington, D. C. The immediate 
objectives of this training are to familiarize geologists with the basic principles 
of photogeologic interpretation and with the various photogrammetric instru 
ments used in photogeologic study. The long-range objective of this training is 
to stimulate interest in and use of photogeologic-photogrammetric procedures 
in geologic mapping. 
La photogéologie au bureau géologique des Etats-Unis 
(U. S. Geological Survey) 
La photogéologie au Bureau Géologique des Etats-Unis (U. S. Geological Survey) est discutée 
au point de vue fonctionnement, recherche et instruction. Les photogéologues travaillent sur de 
nombreux projets entre autres étude stratigraphique et structurale de régions de roches bien ou 
mal exposées, étude de la structure géologique de terrain ignéo-métamorphique boisé, étude de 
régions minières spéciales et d’emplacements pour barrages, ainsi que compilation de cartes 
»isopachous». 
La recherche photogéologique est divisée en trois groupes, notamment: 1) le dessin des instru 
ments et leur adaptation aux problèmes photogéologiques; 2) l’étude à l’aide de la photographie 
aérienne de problèmes géologiques choisis; 3) progrès dans les types de films et leur adaptation 
aux problèmes géologiques. 
L’instruction en photogéologie a le double but de rendre les géologues familiers avec les principes 
fondamentaux de l’interprétation photogéologique, et avec les divers instruments photogrammé 
triques employés pour l’étude photogéologique. Cette étude est conduite formellement à Menlo 
Park, Californie, et à Denver, Colorado, et irrégulièrement à Washington, D. C. L’objectif final de 
cette instruction est d’encourager l’intérêt et l’emploi des procédés photogéologiques et photo 
grammétriques dans la cartographie géologique. 
Mr. J. Davidson read a paper by Mr. B. H. Kent, of U.S.A., on Status of 
Aerial Color Photography in Geologic Studies of the U.S. Geological Survey: 
This report on the status of aerial color photography in geologic studies of the 
U. S. Geological Survey is based primarily on field evaluations made in Death 
Valley, California, one of thirteen color-test areas flown in 1955. The aerial color 
photographs of Death Valley are vertical photographs at a scale of 1:10 000 
with 9-inch-square format and normal stereoscopic overlap. Panchromatic and 
infrared vertical photographs (1:10 000 scale) of the test area were also avai 
lable. 
In the study of this color photography some geologic problems were recognized 
that were not apparent on the panchromatic or the infrared photographs, as 
they involved color clues. It was found from field study that high-quality aerial 
color photography increased the extent and reliability of photogeologic interpre 
B. II. Kent, Status of 
Aerial Color Photography 
in Geologic Studies of the 
U.S. Geological Survey. 
(Publ. VII Kl)