Abstract
EVIDENCE concerning geological formations near the surface of the earth, and down to depths of, say, less than one mile, can be obtained by geologists by examining the strata immediately accessible at the surface, and by inference from known similar formations, by skilfully extrapolating down to the required depth. When this process becomes somewhat risky and the formations are economically important, the sinking of boreholes at carefully selected critical places is then undertaken. These, however, are normally costly, and in their place, many companies have undertaken in recent years the geophysical surveys which, though less costly than the sinking of boreholes, have provided just that extra information which the geologist required, and that in reasonable time.
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Geophysical Exploration in Canada and the United States. Nature 153, 503–504 (1944). https://doi.org/10.1038/153503a0
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DOI: https://doi.org/10.1038/153503a0