MEMORIAL OF ARNOLD HAGUE 37 



noted that in 1851 Bunsen had suggested the hypothesis of a pyroxenic 

 magma and a feldspathic magma as the sources of all intermediate vol- 

 canic rocks, which might be formed by their mixture — an idea he had 

 gotten from studying the basaltic and rhyolitic lavas of Iceland. It is 

 probable that Hague became acquainted with this theory directly from 

 Bunsen, which may account for the hold it had on him in later years, 

 though he never advocated it directly. From Heidelberg he went to the 

 Bergakademie in Freiberg, Saxony, in the spring of 1865, where he met 

 for the first time S. F. Emmons, who had been there the previous year. 

 This was the beginning of another friendship which was to continue 

 throughout life and was to influence the careers of both these embryo- 

 geologists, who were within four months of the same age. Emmons, 

 having had a year's experience at the Bergakademie, became the adviser 

 of Hague as to his best course and joined him in all the week-end excur- 

 sions with von Cotta, visiting many parts of Saxony and studying petrol- 

 ogy according to von Cotta's text-book. Their evenings were often spent 

 studying the geological map of Saxony, and thus acquiring their initial 

 experience in geological cartography. In a reference to this experience 

 Hague has said : "Both came to realize the influence of Cotta on our 

 future careers, as he gave us much of his time.'' ^ 



Bernhard von Cotta was the author of a text-book of petrography, "Die 

 Gesteinslehre," the second edition of which was published in 1862, and 

 this book became Hague's guide and basis of petrography. In it all rocks 

 were classified according to mode of origin : as eruptive, metamorphic, or 

 sedimentary ; and eruptive rocks were divided into two groups on a chem- 

 ical basis : 1, those poor in silica, or basic ; 2, those highly siliceous, or 

 acid. Each group was further divided into volcanic and plutonic. The 

 separation into basic and acid appears to have been made with Bunsen's 

 hypothesis in mind, but not directly as an expression of it, for von Cotta, 

 in 1858, had proposed the hypothesis that the solid crust of the earth 

 consisted of highly siliceous substances, and that the fluid portion be- 

 neath had about the composition of the most basic rocks, and that the 

 variations in composition of eruptive rocks were due to the variable 

 amounts of the solid siliceous crust which was taken up by the basic 

 magma during its passage toward the surface of the earth. 



Although Sorby had made the first use of the microscope in studying 

 rock sections in 1851, and Zirkel had published microscopical descrip- 

 tions of rocks in 1863 and 186-1, the application of the microscope to 

 petrography had not attracted any attention when Hague was preparing 



2 Arnold Hague : Biographical memoir of Samuel Franklin Emmons. NatioUal Acad- 

 emy of Sciences, vol. ii, 1913, p. 315. 



IV— Bull. Geol. Soc. Am., Vol. 29, 1917 



