The Beginnings of Microscopic Petrography in the United States, 1870-1885

In the 1860's and 70's, microscopic petrography flourished in Germany, where descriptions and classifications of rocks were highly valued for their own sake. American geologists, however, were more interested in stratigraphical correlations and had relatively little use for petrographical details. Thus, such Americans as George Hawes and Alexis Julien, who attempted to introduce the microscope for purely petrographical work in the early 1870's, had great difficulties in finding an audience. During the late 1870's, however, a number of American geologists-including federal geologists working amongst the volcanic rocks of the West, state geologists mapping in the Lake Superior region, and mining geologists examining the Comstock Lode and the Leadville district-came to appreciate the aid microscopic petrography could provide for stratigraphical correlations. This growing interest led to the hiring of a number of microscopic petrographers around 1880. These petrographers were trained in Germany, where they had imbibed the German passion for petrography for its own sake, but most of them adapted themselves to the American practice of using petrography for stratigraphy. Unlike many of their German counterparts, these American petrographers spent a substantial portion of their time in the field and combined mapping with microscopic examinations to solve stratigraphical problems. Thus, the different scientific cultures of Germany and the U.S. significantly affected the ways in which the petrographic microscope was used.