After-effects of igneous intrusion
Development of microscopic Petrography in the last fifty Years A backward look over the course of geologic thought and interest in North America during the life of our Society, and perhaps for ten or fifteen years earlier, brings into the foreground some striking features. A span of years of this duration is not beyond the personal recollections of some of the Fellowship and not beyond the personal participation of a few who are still active. One recognizes at once the entrance into general use of the polarizing microscope and the consequent widespread study of rocks in thin sections. Although this method of investigation was cultivated in this country in the decade of the seventies by A. A. Julien, C. E. Wright, E. S. Dana, J. H. Caswell, George W. Hawes, B. K. Emerson, M. E. Wadsworth, and perhaps one or two others; and although stimulated by Zirkel’s volume in the . . .