276 F. D. Adams — New Nepheline Rock. 



The Mode, or actual mirier alogical composition of the rock, 

 is quite different from the Norm, as given above, no leucite, 

 anorthite, olivine, or akermanite being actually present. The 

 mode is abnormative* to a striking degree. 



The Mode is as follows : 



Albite '. 1-83 



Nepheline 72*20 



Sodalite -28 



Cancrinite ._ 5*14 



Hornblende 15*09 



Hematite i *50 



Calcite 312 



Pyrite *14 



98-30 



Water -50 



Excess of A1 2 8 1*20 



100-00 



In calculating this mode the nepheline is taken as consisting 

 of soda nepheline and kaliophyllite, in the proportions of 5 to 1, 

 which is the composition of the nepheline of the nepheline 

 syenite occurring further to the west in the area of the township 

 of Dungannon.f One-half of the water found in the analysis 

 is considered as being present in the cancrinite, the remainder 

 being regarded as belonging in part to the hornblende and as 

 existing in part as hygroscopic water. This gives cancrinite 

 in about the proportion in which it seems to be present in the 

 thin sections of the specimens analyzed. 



The various bases not required by the other minerals and 

 remaining over to form the hornblende, are present in the pro- 

 portions required to form syntagmatite ; which are the propor- 

 tions in which these bases are found in the hastingsite of the 

 Dungannon nepheline syenite. The hornblende has accordingly 

 been calculated as syntagmatite, using the theoretical values 

 given by Zirkel : Lehrbuch der Petrographie, vol. i, p. 303. 

 This accounts for the existing percentages of all the constituents 

 of the rock, with the exception of an excess of 1*20 per cent 

 of alumina. 



Of the rocks hitherto described, those which bear the closest 

 resemblance to Monmouthite are the Urtites of the Peninsula 

 of Kola.;}; These, however, belong to the class of the Dosalanes. 



Geological Department, McGill University, Montreal, P. Q. 



* See Quantitative Classification (loc. cit.), p. 150. 

 f B. J. Harrington : loc. cit. 



\ W. Ramsay : Das Nephelinsyenitgebiet auf der Halbinsel Kola, Fennia. 

 15^ No. 2, p. 22. 



