CLASSIFICATION OF IGNEOUS ROCKS 59 



in the report of the Canadian Geological Survey is calculated from 

 the analysis, the actual mineral composition is probably also repre- 

 sented by it. The craigmontite type contains muscovite, but the 

 name may be applied, with a proper prefix, to any oligoclase- 

 nephelite rock of Family 30, for example aegirite-craigmontite, etc. 



CLASS I,* ORDER 3 



(139) Leucogranogabbro. While adam-gabbro would be more 



correct than granogabbro for the rocks of this family, the term is 

 objectionable in sound, and, furthermore, since granodiorite is so 

 firmly established that it must be retained, granogabbro as an 

 analogous term should also be retained. See note under grano- 

 diorite (229). 



Leucorhyobasalt. For the same reason that rhyodacite 

 is retained rhyobasalt is used. See note under (229), Strictly 

 speaking the term should be leuco-rhyo-quartz-basalt, but the prefix 

 "rhyo-" may be considered as indicative of the presence of quartz. 

 (13 10) Quartz-anorthosite. See note under (13 15). 



Leuco-quartz-basalt. The extrusive of the above. 



(1314) Leucomonzogabbro. The objection to syenodiorite, 

 mentioned under (1214), applies also to syenogabbro, which was 

 previously proposed by the writer.^ That term is now withdrawn 

 and monzogabbro is substituted. See note under (2314). 



(13 1 5) Anorthosite Hunt. The term anorthosite was pro- 

 posed by T. Sterry Hunt^ for rocks composed chiefly of plagioclase 

 (labradorite in most Canadian occurrences). The name is derived^ 

 from anorthose, originally used by Delesse for triclinic feldspars, 

 although now used for anorthoclase. Anorthosite, consequently, 

 properly should not be applied to plagioclase rocks. It is in 

 such general use, however, that it must either be dropped entirely 

 or else used in the sense of Hunt. Turner^ would apply the term 



* Albert Johannsen, "Suggestions for a Quantitative Mineralogical Classification 

 of Igneous Rocks," Joiir. Geol., XXV (191 7), 89. 



^ T. Sterry Hunt, Geology of Canada (Montreal, 1863), p. 22. 



3 Frank D. Adams, "tjber das Norian oder Ober-Laurentian von Canada," 

 Neues Jahrb., B.B., VIII (1893), 423. 



<H. W. Turner, "The Nomenclature of Feldspathic Granolites," Jour. Geol., 

 VIII (1900), 106-11. 



