232 Canadian Record of Science. 



submitted, considers the feldspars composing them to be 

 microcline, and in part microcline-microperthite, with 

 probably some anorthoclase. 



The specific gravity of these phenocrysts was deter- 

 mined in the case of two hand specimens of the pulaskite 

 from different parts of the mountain. In the first of these 

 three specimens 0/ the feldspar were found to have specific 

 gravities of 2.62, 2.609, and 2.603, respectively ; while in 

 the second, five specimens of the feldspar were selected 

 and found to have specific gravities lying between ortho- 

 clase and albite, which bears out the results of their 

 microscopic study. 



The smaller lath-shaped feldspars, although more 

 frequently composed of a single species, often show an 

 intergrowth of two feldspars, as described in the case of 

 the phenocrysts. Separations of the constituents of 

 several species of the rock by means of Thoulet's solution 

 show that these smaller feldspars have a somewhat lower 

 specific gravity than the phenocsysts. Thus, while the 

 specific gravity of the phenocrysts lies between 2.591, 

 and 2.62, that of the smaller feldspars is between 2.591 

 'and 2.56 ; that is to say, the smaller feldspars approach 

 more nearly to pure orthoclase in composition. They 

 consist chiefly of minute intergrowths of orthoclase with 

 albite, or of either of these with microcline or anorthoclase. 

 No lime-soda feldspar could be recognised in any specimen 

 of the rock. 



Nepheline and sodalite. — These minerals are quite sub- 

 ordinate in amount, although they are seen in nearly 

 every thin section. Both minerals present the same 

 characters and occur in the same way as the essexite, 

 lying chiefly in the corners between the other constituents 

 being penetrated by the latter, but also occurring as 

 inclusions in the feldspar. They are, as a general rule 

 much altered as to the same decomposition product seen 

 in nepheline in the essexite and which is as has been 



