CLA SSIFICA TI ON OF IGNE OUS RO CKS 633 



nate ones, we see from the norm that the pyroxenes and olivine 

 are together dominant over the non-silicates, magnetite and 

 ilmenite, the apatite being in negligible amount. The Grad is 

 therefore the second, and this might be called mo?izonate. 



Coming to Subgrad, we have to deal with the chemical char- 

 acter of the femic minerals. This is (Mg, Fe)0: CaO" :: 0.160: 

 0.094=1.702. The Subgrad is the second, domiric, and this 

 might be named monzonote . 



Taking up next the mode and texture, it has been seen that 

 the mode is normative as far as the salic minerals are concerned, 

 but that hornblende, with a little biotite, largely replaces the 

 normative femic minerals. Hornblende is therefore the critical 

 mineral and biotite the varietal. The texture is simply a normal 

 granitic one and rather coarse, for which we use the term 

 grano. 



In the field, then, the rock would be referred to either its 

 Class, as biotitic hornblende-grano-dosalane, or its Order, as biotitic 

 hor?iblende-germa?iare, or as a grano- hornblende-germa?iare, if we 

 wished to disregard the small amount of biotite and emphasize 

 the hornblende content. 



Further study with the microscope and in the laboratory 

 would allow us to speak of the rock as grano- hornblende-mo?i- 

 zonase, or biotitic hornblende-grano-monzonose, according to what 

 information we wished to convey. 



The augite-latite of the Dardanelle Flow, in Tuolumne 

 county, California, 1 which belongs to the same Subrang, would 

 be spoken of as normative phyro-mo?izo?iose , since the augite is 

 almost wholly diopside. Since, however, in the norm of this 

 rock pyroxene and magnetite are present in equal amounts, it 

 would belong to the third Grad, which might be called darda- 

 ?iellate. 



Similarly, confining ourselves to the same Subrang, the 

 olivine-trachyte of the Arso, in Ischia, would be olivinic-phyro- 

 monzonose, the gauteite of Hibsch 2 , a hornblende-trachiphyro-mon- 



•F. L. Ransome, A. /. S., Vol. V, p. 363, 1898. 



2 J. E. Hibsch, T. M. P. M., Vol. XVII, p. 84, 1897. 



