Geological ideas from the beginning have clustered on a succession of concerns which can be related generally to social and industrial pressures. Some concerns, in response to contemporary stimuli, swelled explosively into well-defined constellations of activity to which names such as "creation," "evolution," and "conservation" apply. Other culminations of geological activity, more limited in their reference, relate to changes in technical capability, and seem to last about a quarter of a century.

Always present in geological thought, there has existed an attitude of special relationship to the earth; the geologist is an intermediary between his culture and its physical substructure. The actions of geologists in our civilization have profoundly altered concepts of secular time, the church, man, and the balance of nature. In the last, social pressure must be near its peak.

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