46 REPORT OF COMMISSION VII
United States was the initiation, in the middle thirties, of the widespread pro-
gram of air photography sponsored by the Department of Agriculture. Although
intended primarily for purposes of agricultural engineering, a wise decision to
: sell photos for the mere cost of reproduction broke down economic barriers and
brought the benefits of aerial photography within reach of a broad group of
potential users. Scattered workers in the various fields of earth science were
quick to exploit the advantages of photo-interpretation for their research, and
numerous publications based thereon appeared in print. Owing, however, to the
inertia of traditional ways, to lags in the dissemination of information, and to
various misunderstandings, possibilities were far from fully exploited during
this period. The progress actually made, nevertheless, is reflected in the papers
by van Nouhuys (1937) and Loel (1938), concerned with general geology, and by
Levings (1944) in the field of mineral exploration.
The period of World War II gave enormous impetus to photo-interpretation.
Although objectives were narrowed, facilities and resources were greatly ex-
panded in response to military requirements, and the pressing demands for
speed and effectiveness in gathering various types of information led necessarily
to the widespread adoption of photo-interpretation procedures, and the training
of innumerable workers in the various phases of interpretation. Although much
of the effort was directed specifically toward military installations and activities,
a substantial part had to do with terrain in its various aspects, and thus had a
distinctly geologic flavor. Many geologists, furthermore, were drafted into photo-
interpretation work which, although of a non-geologic nature, did provide op-
portunity to become familiar with photos and learn of their possibilities for
scientific pursuits. Still another product of the war period was the publication
of two textbooks (Eardley, 1942, and Smith, 1943) concerned with geologic
aspects of photo-interpretation.
Following the war there came what might be termed a period of consolida-
tion and standardization. As a result of widespread training in the use of photos
and the extensive publicity given photo intelligence, during the war, pre-war
difhdence toward photo-interpretation in many quarters was quickly overcome,
and there grew a general recognition of its value as a practical working tool
in the various fields of earth science. Academic, commercial, and governmental
workers alike took advantage of the ‘‘new’’ technique, with the result that pro-
cedures were more or less standardized, and capabilities, together with limita-
tions, were more clearly defined. Training in the use of air photos, meanwhile,
was introduced in the more progressive colleges and universities, with the result
that the younger generations of professional earth scientists begin their careers
amply equipped to make full use of photo-interpretation in all situations where
it is applicable. Thus we may say that today photo-interpretation has taken its
place along with such other standard techniques as the use of the microscope and
the plane table.
USE OF AIR PHOTOS IN EARTH SCIENCE
Having thus reviewed general trends, it is appropriate to consider in some-
what greater detail the progress made in each of the main fields of earth science.
In geomorphology, the applications of photo-interpretation have been particu-
larly fruitful. Detailed studies of individual areas have been greatly expedited,
and varieties of landforms previously unknown have been distinguished. One
of the first regional studies utilizing photos was that of Bretz (1932) on the
Grand Coulee of Washington. In the following year, Melton and Schriever
(1933) used photos to ascertain, for the first time, the distribution and unique
characteristics of the Carolina “Bays,” shallow oval depressions of systematic
