AIR CRAFT IN THE STUDY OF ROCKS AND ORES
(FIG. 53)
The admirable manner in which air photography lends itself to the
observation of geographic relations and physiographic processes suggests
its use as a valuable addition to the instruments of geologic
reconnaissance; for, not only is the study of geology inseparable from
that of physiography, but, in large measure, geology is applied physical
geography and many conclusions of a geologic nature are drawn from
observed surface relations.
Probably, in most cases, the actual character and composition of rocks
cannot be determined from air photographs; but, just as on a good map an
area of crystalline rocks can be distinguished from one of sedimentary
rocks by means of the topographic expression, so areas of different
rocks can be distinguished on photographs. For instance, an area of
upturned sedimentary rocks would be readily distinguished from one of
horizontal rocks. Figure 42 shows how the character of glaciated
mountains is revealed, and Figures 37 to 41 of the Michigan area show
well the familiar features of continental glaciation.
It is perhaps premature to say much of the use of the airplane in the
study of geology until it has been thoroughly tested. But it should be
possible from the air to locate and map ore bodies, metalliferous veins,
and outcrops of rock: for it is well known that rocks at the outcrop
differ in color, in the forms of erosion developed in them, and in the
kind of plants which they support. It is of interest that Colonel Alfred
H. Brooks, who was Chief Geologist of the American Expeditionary Forces
in France during the war, found that geologic boundaries could be
recognized on air photographs and that by means of these photographs he
could correct existing geologic maps and identify
[Illustration: FIG. 53--Canyon in sedimentary rocks near the mouth of
the Pecos River, Texas. The rocks consist of flat-lying strata, and the
tortuous lines resembling the grain in wood denote the outcrops of hard
layers and the benches formed on these layers by erosion. This
photograph illustrates the use of air photography in geological
reconnaissance. Scale not known.]
formations in inaccessible areas within the enemy lines. His method was
to use air photographs in the study of the geologic formations of areas
accessible to him. Then, having familiarized himself with the appearance
of the different rock formations and structures on the photographs, he
was able to recognize the same features on photographs of areas held by
the enemy and so project his mapping over into inaccessible
territory.[4]
The prospector should effect a great saving of time by using air
photographs to guide him to places where he can find exposures of rock
and to help him to avoid places where it would be useless to look for
exposures. Particularly in wooded regions air photographs are valuable
in indicating localities where exposures can be found in areas so
covered with forest that examination on the ground would not be worthy
of consideration. Prospectors for oil are planning to use airplanes for
this purpose in northern Canada, in South America, and in other places
where much of the country is so densely wooded that much time is usually
spent in looking for clear space.
USE IN EXPLORATION
Exploratory work should benefit in many ways. General reconnaissance has
been carried on to a considerable extent in foreign lands with airplanes
and to some extent also in America. Wide areas along the Mexican border
have been photographed for the making of new maps and for the correction
of existing maps. The same photographs would be useful in geologic
reconnaissance. The new photographs of southern Arizona are said to show
mountain ranges many miles away from their location on existing maps.
Such corrections are of importance to the geologist as well as to the
geographer and the map-maker. Amundsen intends to employ several small
planes in his Arctic work now under way. Mjöberg[5] has projected an
expedition to New Guinea in which the use of airplanes is a fundamental
condition.