CLASSIFICATION OF IGNEOUS ROCKS i6i 



characteristic texture of this rock excludes it from representing 

 the family. 



(2121) Ortho-nephelite-syenite, ortho-leucite-syenite. This is 

 nephelite- (or leucite-) syenite without plagioclase. 



Orthofoyaite. See note under (2222). 

 Orthoditroite. See note under (2222). 

 Orthophonolite. The extrusive equivalent of the pre- 

 ceding. 



(2122) Albite-nephelite-syenite, albite-leucite-syenite. Nephe- 

 lite- (leucite-) syenites carry orthoclase either as the only feldspar 

 or in combination with plagioclase, which may be albite or some 

 other member of the series. In this family (2122) belong those 

 carrying albite. 



Albite-foyaite. See note under (2222). 

 Albite-ditroite. See note under (2222). 

 Albite-phonolite. The extrusive corresponding to the 

 preceding. 



(2123) Albite-nepheKte-monzonite. Here belong numerous 

 tinguaites and so-called nephelite-syenites, also a sodalite-foyaite 

 and a cancrinite-syenite. Covite Washington, according to the 

 calculated mode, belongs here, but under the definition Washington^ 

 says the rock is a "leucocratic combination of orthoclase and less 

 nepheUte with hornblende and aegirite-augite," which would place 

 it in Family 21. 



(2124) Litchfieldite Bayley. In his description of litch- 

 fieldite Bayley^ says: "As was indicated by the microscopic study, 

 no plagioclase other than albite is present, and this, as seen (from 

 a calculated mode), is largely in excess of the orthoclase."' The 

 mode computed from the analysis indicates 27 per cent ortho- 

 clase and microcline, 47 per cent albite, 17 per cent nephehte, and 

 2 per cent cancrinite. These proportions are about the same as 

 shown by the thin section and Thoulet separation. While cancri- 

 nite occurs in the type rock, Bayley^ says: "I do not regard 



^ Henry S. Washington, "The Foyaite-Ijolite Series of Magnet Cove: A Chemical 

 Study of Differentiation," Jour. GeoL, IX (1901), 615. 



^W. S. Bayley, " Eleolite-Syenite of Litchfield, Maine," Bull. Geol. Soc. Amer., 

 Ill (1892), 242. 



^ Ibid., In Utteris, June 14, 19 19. 



