The application of geophysics to mining problems is much more difficult than is the case with the petroleum industry. The fundamental contrasts between the occurrence of petroleum and ores are outlined. Difficulties arise because of the great complexity and variation in occurrence and size of deposits of commercial metallic and non-metallic minerals. These complexities are discussed and illustrations cited in terms of mineralogic, petrographic, structural, and genetic variations in ores. The relatively large horizontal extent of petroleum deposits, as compared with many mineral deposits is emphasized.One of the important problems in the application of geophysics to ore-finding is determining the definite relation of ore to specific geologic features, so that the results of geophysical work can be interpreted in terms of the probable location of more ore. This is essentially a geologic problem, and one not easily solved in many districts. For the successful application of geophysics and interpretation of the results, a very detailed knowledge and understanding of the geology is fundamental. Also additional geophysical methods are required, particularly those which might locate ore directly rather than indirectly through the geology as is largely the case in petroleum.Because of the complexities involved, no one method should be considered a true test of an area but several methods should be utilized. Much more extensive and intensive application of geophysics to problems of ore-finding, as well as new methods are demanded by the rapid depletion of present ore reserves.