176 ALBERT JOHANNSEN 



under the names Eleolith-Syenit and Nephelin-Syenit, rocks which 

 had previously been described as zircon-syenite, foyaite, miascite, 

 and ditroite. If these terms were not acceptable he suggested that 

 all of the rocks of this class be included under foyaite, since the 

 rocks from Mount Foya, in the Serra de Monchique, province of 

 Algarva, Portugal, as originally described by Blum/ are most 

 nearly representative of the whole group. The term eleolite has 

 fallen away, more or less, since the age element in mineralogy is no 

 longer considered, and in general, in this country, the rocks have 

 been called nepheHte-syenites. Brogger^ proposed to subdivide 

 the nephelite-syenites into two groups according to texture. For 

 rocks of this composition and with trachytoid texture he used 

 Blum's term foyaite, and for those with granitic texture Zirkel's^ 

 term ditroite. In the present classification, under the term 

 nephelite-syenite, are included those nephelite-bearing rocks in 

 which orthoclase exceeds acid plagioclase (oligoclase or andesine) 

 in amount. The rocks in which the plagioclase is albite are here 

 called albite-nephelite-syenites (2122), and those which contain no 

 plagioclase, ortho-nephelite-syenites (212). 

 Foyaite Blum-Brogger. 



Ditroite-ZlRKEL-BROGGER. 



Syenoid Shand. As an abbreviation for feldspathoid- 

 syenite, Shand'' used syenoid, and said the term would "imply the 

 presence of nephelite. " He further suggested that gabbroid, 

 dioroid, and doleroid might be advantageously coined in the same 

 manner. Syenoid could well be used as a family name to include 

 both nephelite and leucite rocks. 



Leucite-syenite. 



^ R. Blum, "Foyait, ein neues Gestein aus Siid-Portugal," Neues Jahrh. (1861), 

 p. 426. 



= W. C. Brogger, op. ciL, Zeiischr. f. Kryst., XVI (1890), pp. 39, 125; also Die 

 Eruptivgesieine des Kristianiagehietes. Ill: Das Ganggefolge des Laurdalits (Kris- 

 tiania, 1898), pp. 164-65. 



3 F. Zirkel, Lehrbuch der Petrograpkie (ist ed.; Bonn, 1866), I, 595. The term is 

 derived from Ditro, in eastern Siebenbiirgen, Transylvania. 



'' S. J. Shand, "On Borolanite and Its Associates in Assynt," Trans. Edinburgh 

 Geol. Soc, IX (1910), 377. 



