234 Canadian Record of Science. 



The mode of the Mount Johnson pulaskite (No. VII), 

 calculated from the analysis given above, is as follows : 



Albite - . - - 

 Anorthite 



48.73) 

 - 3.06 [74.03 



Orthoclase and microline - 



22 24 1 



Nepheline 



2.56 



Kaolin - 



4.96 



Hornblende - 



5.08 



Biotite - 



6.29 



Magnetite 



Ilmenite ... - 



• 1-861 ~ L. 

 0.91/ 2 " 



Sphene - - - - 

 Apatite .... 

 Water (hygroscopic) 



2.35 

 1.34 

 0.30 



99.68 

 This proportion of the various minerals expresses 

 exactly the chemical composition of the rock as presented 

 by the analysis, except that a very small excess of silica, 

 amounting to 0.06 per cent., is required. 



The calculation shows clearly the fact, ascertained by 

 the study of the thin sections of the rock, that a consider- 

 able percentage of sphene is present, a mineral which does 

 not occur at all in the essexite. 



The anorthite is probably in combination with the other 

 feldspathic constituents in the form of anorthoclase. The 

 calculation also brings out clearly a point already 

 mentioned, namely, that in this rock the nepheline is 

 much more highly altered than in the essexite, as shown 

 by the amount of kaolin present. This kaolin, however, 

 is not entirely derived from the alteration of the nepheline, 

 but appears as a haze through all the smaller feldspars, 

 and hence in the extension of the results should be 

 assigned in part to the nepheline and in part to the 

 feldspar. It is, of course, impossible to measure the 

 amount of kaolin present by Rosiwal's method, occurring, 

 as it does, distributed through the sections in the form of 

 extremely minute individuals. If, however, the amount 

 of nepheline given by the Kosiwal measurement be 



