CLASSIFICATION OF IGNEOUS ROCKS 169 



granodioritic extrusive, and rhyobasalt is here proposed for the 

 granogabbroic. Syenodiorite and syenogabbro will be replaced by 

 the better terms monzodiorite and monzogabbro. For the corre- 

 sponding extrusives, ande-latite and basa-latite are here proposed. 

 Rhyodacite Winchell/ See note under granodiorite 

 above. This is the extrusive equivalent of granodiorite. 

 (2210) Tonalite VOM Rath-Brogger-Spurr. Tonalite was ap- 

 plied by vom Rath^ to a certain rock from Monte Tonale, in the 

 Tyrol. It consists of abundant quartz, andesine, very small 

 amounts of orthoclase as an accessory, and a dark mineral. In the 

 definition, however, vom Rath omitted the orthoclase, which occurs 

 as micropegmatite and was regarded simply as an accessory, and 

 said: "Der Tonalit enthalt in kornigem Gemenge als wesentliche 

 Bestandtheile: eine trikline Feldspath-Species, Quarz, Magnesia- 

 glimmer und Hornblende." In his tabulation Brogger^ used tona- 

 lite for acid quartz-diorite, and in another place"* he said: ''Der 

 Name Tonalit ware dann den Quarzdioriten vorbehalten." Since 

 Brogger does not use the subdivision granodiorite, his tonahte 

 includes some of these rocks. Simply as quartz-diorite the term 

 was used by Spurr,s who adopted it as a group name instead of 

 quartz-diorite, because it "is shorter and more characterizing." 

 In the same sense it was used by Winchell^ and Hatch,'' and it 

 is so used here. 



Incidentally, the average igneous rock of Clarke,^ computed 

 into common minerals, falls in this family. It contains quartz 



' Alexander N. Winchell, " Rock Classification on Three Co-ordinates," Jour. Geol., 

 XXI (1913), 214. 



^ G. vom Rath, "Beitrage zur Kenntniss der eruptiven Gesteine der Alpen," 

 Zeitschr. d. d. geol. Ges., XVI (1864), 250. 



W. C. Brogger, Z>ze Eruptiv gesteine des Kristianiagehietes . II: Die Eniptionsfolge 

 der triadischen Ertiptivgesteine bei Predazzo in Sudtyrol (Kristiania, 1895), p. 60. 



* Ibid., p. 61. 



s J. E. Spurr, "Reconnaissance in Southwestern Alaska in 1898," U.S. Geol. 

 Surv., Ann. Rept., XX, Part VII (1900), p. 190. 



^Alexander N. Winchell, "Rock Classification on Three Co-ordinates," Jour. 

 Geol., XXI (1913), 214. 



7 F. H. Hatch, The Petrology of the Igneous Rocks (London, 1914), p. 195. 



^ F. W. Clarke, "Data of Geochemistry," U.S. Geol. Surv., Bull. 4gi (1911), p. 31. 



