i68 ' ALBERT JOHANNSEN 



equal portions, one each for normal granite, quartz-monzonite, 

 and granodiorite. 



The term granodiorite is not the most satisfactory, from the 

 standpoint of the construction of the word, for a rock inter- 

 mediate between quartz-monzonite (adamellite) and quartz-diorite 

 (tonalite) , for it suggests a rock intermediate between a granite (an 

 orthoclase-quartz-bearing rock) and a diorite (a plagioclase-quartz- 

 free rock), that is, a quartz-monzonite. Monzonite in the sense in 

 which we now use it, however, was not introduced by Brogger until 

 1895, while granodiorite was first used in 1892 or 1893. The term 

 was intended to convey the idea of a diorite with granitic characters, 

 that is, with quartz and a certain amount of orthoclase, but upon 

 the introduction of the term monzonite Lindgren^ found it advis- 

 able to restrict the "definition of granodiorite to rocks considerably 

 nearer quartz-diorite than originally intended." A name derived 

 from the rocks between which granodiorite, as now defined, actually 

 stands would give adam-tonalite, which is hardly euphonious, to say 

 the least. Furthermore, the term granodiorite is so firmly estab- 

 lished and was so clearly defined that it should not be changed. 



The term banatite was used by Brogger^ for his intermediate 

 quartz-monzonites, and under this term are included rocks which 

 are probably to be classed as quartz-poor granodiorites (see 

 under 2213). 



The objection to the construction of the word granodiorite as 

 applied to rocks under the present definition applies also to the 

 terms introduced by the present writer^ in 191 7, namely grano- 

 gabbro, syenodiorite, and syenogabbro. But since granodiorite 

 is retained for the reasons stated above, and adam-gabbro is as 

 objectionable as adam-diorite, granogabbro (239) also will be 

 retained to make analogous terms. The names of the extrusive 

 rocks should naturally conform in construction to their deep-seated 

 equivalents; consequently rhyodacite Winchell is used for the 



^Waldemar Lindgren, In litteris, June 17, 1919. 



2 W. C. Brogger, Die ErupHvgesteine des Kristianiagebietes. II: Die Eruptionsfolge 

 der triadischen ErupHvgesteine bei Predazzo in Siidtyrol (Kristiania, 1895), p. 60. 



3 Albert Johannsen, "Suggestions for a Quantitative Mineralogical Classification 

 of Igneous Rocks," Jour. GeoL, XXV (1917), P- 89. 



