18 Morey & Bowers— Melting Potash Feldspar. 



The igneous massif of Bezavona in Madagascar , as 

 described by Lacroix, consists of quartz syenites, nephe- 

 lite syenites, monzonites, and other types, including vari- 

 ous dike and flow rocks. In the coarse granular rocks 

 there is apparently nothing suggesting the formation of 

 leucite, but in quickly chilled facies, which may be 

 regarded as quenched, leucite appears. Thus there are 

 microsyenites with leucite and also leucite phonolites. 16 

 These facts again suggest the possibility that the forma- 

 tion of leucite may have been an intermediate step in the 

 genesis of the nephelite rocks. 



Fig. 5. 



Lujavrites "-—'-.-—-.-. .,.--.------ g Kakor tok i fcfi , 



Fig. 5. — Section of the Ilimausak mass, Greenland (afer Ussing). 



Still less definite as evidence, and yet worthy of consid- 

 eration, are certain structures observed in nephelite rocks 

 that suggest the former presence of leucite. In some 

 members of the Ice River complex of British Columbia 

 there are spots of a "finger-print-like" intergrowth 17 of 

 orthoclase and nephelite that is practically identical with 

 the "dactylotype" intergrowth of these minerals when 

 they form pseudo-leucites. Structures that are perhaps 

 of similar origin are described by Lacroix from the nephe- 

 lite syenites of the Los Archipelago 18 and by Brouwer in 

 rocks from the Transvaal. 19 



16 A. Lacroix, Les Boches Alcalines d 'Ampasindava, Nouv. arch, du 

 museum, Paris. Serie 4, 5, 197 and 207, 1903. 



17 J. A. Allan, Geology of the Field Map-area, B. C. and Alberta. Geol. 

 Surv. Han., Mem. 55, p. 133 and p. 285, 1914, Plate XVIIB. 



13 A. Lacroix, Les syenites nepheliniques de 1 'archipel de Los. Nouv. arch, 

 du museum, Serie 5, 3, p. 53, 1911. 



19 H. A. Brouwer, Transvaal Nephelien-Syenieten. p. 40, PL I, Fig. 1. 



