THE BIORITE-AISTDESITE GEOUP 75 



sent very perfect forms. The canerinite occurs both as secondary 

 after the elseolite and as a primary constituent in the form of 

 long needle-like yellow crystals with a hexagonal outline. This 

 last form is especially characteristic of the Litchfield rock. 



Classification and Nomenclature. — Several varietal names 

 have been given to the rocks of this group as described by various 

 authors. Miascite was the name given by 6. Eose to the sye- 

 nite occurring at Miask in the Urals ; Bitroiie to that occurring 

 at Ditro in Transylvania, and Foyaite^ by Blum, to that from 

 Mount Foya, in the province of Algrave in Portugal. The 

 name zircon sye^iiie, or LaiirviUte, has been given to the variety 

 from Laurvig in southern Norway, which is rich in zircons. 

 Tinguaite is the name proposed for a varietal form from Serra 

 de Tingua, province of Rio Janeiro, Brazil. 



American petrographers have not been at all delinquent in 

 the matter of names, and have added to an already over-burdened 

 nomenclature such terms as LitcJifieldite, Ouachitite, Pulaskitej 

 and Fourchite to varieties from Litchfield, Maine, and the Hot 

 Springs region of Arkansas. Lielnerite is the name given to an 

 elseolite syenite porphyry occurring in the Tyrol. 



Rocks of this group, although wide-spread in their distribu- 

 tion, are nevertheless not abundant. The more important 

 localities thus far described have already been noted; there 

 remains to be mentioned the locality at Red Hill, Moulton- 

 borough, New Hampshire, the rock of which was first described 

 as an ordinary syenite, and that of Hastings County, Ontario. 



(2) THE PHONOLITES 



Phonolite, from the Greek word ^(ovij, sound, and ^tdog, stone, 

 in allusion to the clear ringing or clinking sound which slabs 

 of the stone emit when struck with a hannner; formerly called 

 clinkstone for the same reason. 



Mineral Composition, — The phonolites consist essentially of 

 sanidin and nepheline or leucite, together with one or more 

 minerals of the augite-hornblende group, and generally hauyne 

 or nosean. The common accessories are plagioclase, apatite, 

 sphene, mica, and magnetite; more rarely occur tridymite, 

 melanite, zircon, and olivine. The rock undergoes ready altera- 

 tion, and calcite, chlorite, limonite, and various minerals of the 

 zeolite group occur as secondary products. 



