Economic Geology may be practiced in two widely differing ways. Each has its uses and its limitations. First is the meticulous, detailed study of ore occurrences and of the process of ore deposition. This careful work has resulted in nearly all of the progress in the theory of ore deposition, and in the discovery of much of the ore in great districts. Its chief limitation comes from the shortness of human life and the time required for detailed study. Conclusions must either be based on a limited number of observations by one geologist or on observations by several who may have different methods and points of view.The second method, which is the principal subject of the paper, involves rapid and often inadequate visits to many hundred occurrences, with the economic factor always in view. There must be a ground work of thorough study to permit accurate appraisal of essential features. While this method often seems casual, it has resulted in the development of many mines. And the study, even though brief, of many hundred occurrences by one observer may be useful in helping to appraise the theories advanced by those who specialize in detailed research.Examples are given of the variety in occurrence and in probable genesis of many orebodies that seem at first to belong to the same types. Generalizations have usually proved to be either wrong or of limited application.Both methods of practicing Economic Geology are useful. The second, which may be called Comparative Economic Geology, has the added attraction of physical and intellectual adventure.

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