224 Canadian Record of Science. 



This feldspar has the specific gravity and general com- 

 position of an acid andesine, although the high content of 

 K„0 may possibly indicate the presence of some potash 

 feldspar as an intergrowth. 



Nepheline. — This is quite subordinate to the feldspar in 

 amount. It possesses the usual low index of refraction, 

 with extinction parallel to the cleavages, which latter can 

 usually be seen. It is sometimes quite fresh, but at other 

 times is found more or less completely altered to a 

 mineral which occurs as little jibrous bundles, showing 

 strong double refraction and parallel extinction. The 

 fibres usually have a more or less distinctly parallel ar_ 

 rangement. The mineral remains practically unaltered 

 when treated with concentrated hydrochloric acid for 

 twenty minutes, although the nepheline in which it is 

 imbedded is destroyed. It is either muscovite or kaolin. 

 The nepheline is allotriomorphic and occurs chiefly in the 

 corners between the larger crystals of feldspar and other 

 minerals, and is penetrated by them. It is especially 

 abundant in those portions of the rock which are rich in 

 the dark-colored constituents. When occurring in this 

 manner it appears, with the sodalite, to have been the last 

 constituent of the rock to crystallize out. It is usually 

 much more abundant than the sodalite. The nepheline 

 also occurs in places as irregular-shaped lath-like inclu- 

 sions in the feldspar. 



Sodalite is usually, although not invariably, present. It 

 strongly resembles the nepheline in appearance and shows 

 the same alteration product. It is, however, quite 

 isotropic. Like the nepheline, it occurs either in the 

 spaces between the other minerals, cementing them to- 

 gether, or as inclusions in the feldspars. 



Apatite. — The abundance of apatite is a distinct feature 

 in this, as in similar rocks occurring elsewhere. It is 

 always present and was the first constituent to crystallize 

 out, being found in the form of perfect hexagonal prisms 

 with double pyramidal terminations imbedded in the iron 



