CHAPTER XL 



GROUP D. 



NOMENCLATURE. 



r I iHE only indigenous rock belonging to this group, known to occur 

 J- in Britain, is the phonolite of the Wolf Rock, described by 

 Mr. ALLPORT in 187l. (1) Boulders of zircon-syenite (eheolite-syenite) are 

 said to occur in the drifts of East Anglia, but the author is unable to 

 say whether the identification has been made with certainty. Seeing 

 that the group is so poorly represented in Britain it is unnecessary 

 that any detailed description should be given of it in a work like the 

 present. With a view, however, to future eventualities we will give 

 a brief account of its nomenclature and of some of the more important 

 minerals which characterize it. The names zircon-syenite, elseolite-syenite 

 nepheline-syenite, foyaite, miascite, ditroite, teschenite and theralite have 

 been applied to the plutonic representatives of the group, and the names 

 phonolite, tephrite, leucitite, nephelinite, liebenerite-porphyry, gieseckite- 

 porphyry, buchonite, leucite-basalt, nepheline-basalt and basanite to the 

 volcanic representatives. 



Zircon-Syenite. This is an old name introduced by HAUSMANN^ 

 for certain rocks occurring in Southern Norway. It has since been 

 shown that zircon is an accessory mineral, and although very abundant 

 in certain specimens is comparatively rare in others from the same 

 general mass. The name has accordingly been dropped in favour of 

 others, such as augite-syenite and elseolite-syenite, which express more 

 accurately the composition of the rocks. 



Elceolite- or Nepheline-Syenite, The former term is used by ROSEN- 

 BUSCH, the latter by BROGGER and some other authors. Elseolite-syenite, 

 according to ROSENBUSCH, includes all those plutonic rocks which are 

 characterized by the occurrence of orthoclase and elasolite. These two 

 minerals are present in very different proportions in different occurrences, 

 and even in one and the same rock-mass. The ferro-magnesian con- 



(1) G.M., 1871, p. 247, and 1874, p. 462. 



(2) N.J., 1852, p. 712. 



(3) See BROGGEK, Die silurischen Etagen 2 and 3. 



