360 



group is represented, according to ROSENBUSCH, by certain rocks from 

 Montana, U.S.A., described by WOLFF, (I) and also by those teschenites 

 (if any) which contain or contained nepheline. 



Phonolite. Term proposed by KLAPKOTH in place of the old term 

 clinkstone. As used now it generally implies a trachytic texture 

 and the occurrence of sanidine and either nepheline or leucite or both. 

 Many authors restrict it to rocks containing nepheline and sanidine. 

 ROSENBUSCH, however, includes certain rocks without nepheline but 

 containing leucite (e.g., leucitophyres and leucite-trachytes). There are 

 many varieties of phonolite depending on the accessory minerals. These 

 have received such names as leucite-phonolite, nosean-phonolite, leucite- 

 nosean-phonolite, &c. 



Tephrite. This term is used by ROSENBUSCH for the trachytic 

 representatives of the theralites. The tephrites, therefore, are charac- 

 terized, according to this author, by the occurrence of plagioclase and 

 either nepheline or leucite or both. The two principal groups are the 

 nepheline-tephrites and the leucite-tephrites. 



Leucitite. This term is generally used to designate a trachytic 

 rock in which leucite takes the place of felspar, and from which olivine 

 is absent. The olivine-bearing rocks of similar character are termed 

 leucite-basalts. 



Nephelinite. This term corresponds to the preceding with the 

 difference that it is applied to rocks in which nepheline takes the 

 place of felspar. The olivine-bearing rocks are termed nepheline- 

 basalts. 



Liebenerite-porphyry. This term is applied to a rock occurring 

 in the Southern Tyrol. The rock is of trachytic texture and may be 

 described as an altered phonolite. It contains porphyritic crystals of 

 orthoclase and liebenerite (pseudomorph after nepheline) in a compact 

 ground-mass. A similar rock from Greenland has been termed gieseckite- 

 porphyry. Gieseckite and liebenerite appear to be synonyms. 



Buchonite. This term was proposed by SANDBERGER for a rock 

 occurring in the Rhongebirge (North Germany). The rock is composed 

 essentially of nepheline, plagioclase, augite and magnetite and is therefore 

 a nepheline-tephrite. 



Basanite. This term is used by some authors to include the 

 nepheline- and leucite-basalts. 



The rocks of the present group belong to the intermediate and basic 

 divisions so far as silica percentage is concerned. They differ, however, 

 from the ordinary intermediate and basic rocks in containing a very 



(1) Notes on the petrography of the Crazy Mountains, &c. Northern Transcontinental 

 Survey. See also N.J. Ref., 1886, Band I., p. 268. 



