50 REPORT OF COMMISSION VII
going may be considered. It is in petroleum geölogy that these applications are
most widely exploited. Discussion of this and of applications in the other fields
of applied geology, however, is handicapped by the paucity of published infor-
mation. Owing to the confidential nature of much commercial work, and to the
lack of time on the part of geologists engaged in such work, specific accomplish-
ments are not often publicized. The following discussion is therefore based only
on partial information.
Petroleum geology is primarily the application of the principles of structural
geology, stratigraphy, and sedimentation to the search for oil and gas. In so far
as photo-interpretation applies to these fields of basic geology and to general
mapping, it applies also to petroleum exploration. Prior to World War II, photo-
interpretation was employed to a varying extent by some oil companies (Levings,
1944), partly on an experimental basis. One of the larger projects to make effec-
tive use of the method was in the survey of New Guinea in the later thirties
(Helbling, 1949, ch. 10). Subsequent to the war there came a period of rapid
expansion. Procedures were more or less standardized and functions more clearly
defined. The publications of Brundall (1947), Wasem (1949), and Wengerd
(1950) are expressive of the general method of approach, and the paper of De
Blieux (1949) reports on the special problems and criteria employed in the
Gulf Coast region. Problems of structure contouring, a widely used method of
presenting geologic data, are discussed by Nugent (1947) and Desjardins
(1950a,b). Methods for accurate measurement of dip from photos, which fre-
quently is of considerable structural importance, are presented by Desjardins
(1943), Wallace (1950), and Elliott (1952).
In the petroleum industry, photogeologic interpretation seems to have taken
its place along with such other standard exploration methods as geophysics and
surface mapping. At the present time, it is estimated that more than 60 men are
employed in this type of work in the United States, and the number appears to
be increasing. The advantages of speed, economy, and efficiency afforded by
photogeologic reconnaissance mapping have a particular appeal in this highly
competitive industry.
Mining geology also represents the application of basic bedrock geology to a
particular set of practical problems. The application of air photos to these prob-
lems has been reviewed by Gill (1932) and by Levings (1944). A detailed study
of one mining district has been recorded by Reed (1940), and a discussion of
prospecting in a Canadian area with the aid of photos has been presented by
Jolliffe (1945). The limited information now available indicates that photo-
geologic methods and direct aerial observation have been of definite value both
in the discovery of new mineral deposits and in the development of deposits
previously known.
Civil engineering projects utilize both bedrock and surficial geology in the
search for construction materials, in the selection of sites, and in the study of
excavation, foundation, and drainage conditions. The utilization of air photos
in obtaining construction materials has been discussed by Eardley (1943) and
Hittle (1949), and the latter includes other phases of engineering applications.
Case studies in the application of photogeologic methods are very few, one wor-
thy of particular mention being that of Henderson (1939), on tunneling opera-
tions. It appears that in this country the application of photo-interpretation
to geologic engineering problems has been somewhat limited, and that consider-
able opportunity for future development in this field may exist. In arctic regions,
however, the situation is very different. The peculiar and troublesome engineer-
ing problems presented by permafrost, or perennially frozen ground, have de-
manded extensive study. The application of geomorphic methods of investiga-
