CLASSIFICATION OF IGNEOUS ROCKS 229 



Another rock belonging here is the biotite-pyroxenite from New 

 Zealand described by Hutton.^ It consists of biotite and horn- 

 blende in about equal proportions. 



Family 12. — Finally, in Family 12, belong the pure pyroxene 

 rocks, such as diallagite, bronzitite, hypersthenite (together called 

 pyroxenolites by Lacroix).^ Websterite Williams,^ named from 

 Webster, North Carolina, contains both orthorhombic and mono- 

 clinic pyroxenes with accessory iron ores. 



Ilmenite-enstatitite Vogt'* contains as much as 60 per cent 

 ilmenite; consequently it ranges from Order 2 to 3. A magnetite- 

 pyroxenite described by Jennings^ and Bastin^ also belongs to 

 Order 3. It contains 67 . 25 per cent magnetite, 8 . 30 per cent ilme- 

 nite, 16.89 P^r cent diopside or augite, 6.70 per cent spinel, 

 and . 18 per cent apatite. 



APPENDIX 



This appendix might be introduced by the Spanish proverb: 

 "El sabio muda consejo, el necio no," were there no danger of 

 some critic replying with: "Prudentis est mutare consilium; stul- 

 tus sicut luna mutator." 



In the first instalment of this paper (p. 38), the writer spoke 

 of a contemplated change by which seventy-two famihes were to 

 be omitted, but letters sent to a considerable number of petrog- 

 raphers found no uniformity of opinion. Some were in favor 



'F. \V. Hutton, "On a Hornblende-Biotite Rock from Dusky Sound, New 

 Zealand," Quart. Jour. Geol. Soc, XLIV (1888), 745-46; also "The Eruptive Rocks 

 of New Zealand," Jour, and Proc. Roy. Soc. New South Wales, XXIII (1889), Part I, 

 p. IS4- 



^ A. Lacrois, "Sur les roches basiques constituant des filons minces dans la Iherzo- 

 lite des Pyrenees," Comptes Rendus, CXX (1895), 752-55. 



3 George H. Williams "The Non-feldspathic Intrusive Rocks of Maryland and the 

 Course of Their Alteration," Amer. Geol., VI (1890), 40-41, 



-ij. H. L. Vogt, "Bildung von Erzlagerstatten durch Differentia tionsprocesse 

 in basischen Eruptivmagmata," Zeitschr.f. prak. Geol. (1893), p. 8. 



5 E. P. Jennings, " A Titanif erous Iron-Ore Deposit in Boulder County, Colorado," 

 Trans. Amer. Inst. Min. Eng., XLIV (1913), 14-25. 



^ Edson S. Bastin, "Economic Geology of Gilpin County and Adjacent Parts of 

 Clear Creek and Boulder County, Colorado," U.S. Geol. Surv., Prof. Paper g4 (1917), 

 p. 47. 



