40 PROCEEDINGS OF THE SAINT LOUIS MEETING 



induce him, if possible, to visit America and study in the presence of the 

 collectors their collection of rock specimens, for at that time no American 

 geologist had any practical knowledge of this new branch of geology. 

 From this visit resulted Zirkel's volume on microscopical petrography, 

 which marked the opening of a new era in geological study in the United 

 States." 2 



It is interesting to note the phases of petrography through Avhich the 

 work of the Geological Exploration of the Fortieth Parallel passed, since 

 this was the first of the larger surveys in this country that took a deep 

 interest in the petrography of eruptive rocks. It began with King^s 

 interest in the lavas of the Pacific Coast volcanoes and the igneous rocks 

 of the Sierra Nevada. This took definite form through his association 

 with Bajon von Eichthofen during his visit to the Pacific coast, where 

 he studied the Tertiary volcanic lavas and, observing their strong resem- 

 blance to those of Austro-Hungary, w^ote his paper on a National System 

 of A^olcanic Rocks, published in San Francisco in 1868. This gave King, 

 no doubt, his definite conceptions of rock varieties and their order of 

 eruption, which represented the most advanced views of pre-microscopic 

 petrography and placed King in advance of his assistants of von Cotta's 

 school. Under these influences the volcanic rocks of the region surveyed 

 were studied and classified. After the collection had been made and 

 brought to New York, Zirkel, the young creator of microscopical petrog- 

 raphy, was invited to study the specimens in the presence of the collectors, 

 and we have been told he was much influenced by the eloquent and force- 

 ful exposition of King and his associates regarding the nature and occur- 

 rence of the rocks. AVe are led to believe that Zirkel's judgment was 

 warped to some extent in determining the composition of some of the 

 specimens, in particular what were at that time called propylites and 

 trachytes. This opinion would seem to be justified by Zirkel's own state- 

 ment in his letter transmitting the report to Clarence King. The report, 

 written by Zirkel in English, was edited by King and published as Vol- 

 ume yi, in 1876. On its receipt by the geologists of the Survey, appro- 

 priate notes regarding the microscopical characters of particular rocks 

 were inserted in the reports of Hague and Emmons in Volume II, which 

 was printed the following year. In this manner were blended the best of 

 pre-microscopic petrography with the earliest products of microscopical 

 research. 



The results of Hague's geological work in connection with the explora- 

 tion of the Fortieth Parallel are published, with those of Emmons, in 

 Volume II, "Descriptive Geology," each describing those parts of the 



S. F. Emmons : Clarence King. Am. Jour. Sci., 4th ser., vol. 13, 1902, p. 229. 



