lADAMS A HARLOW] ALKALI SYENITES OF EASTERN ONTARIO 38 



stituents. The albite is well twinned and must be a variety approach- 

 ing the pure soda molecule, as it has a specific gravity of 2.618 and 

 shows a maximum extinction against the line of the twinning lamellae 

 of 15°. In a single slide a few grains having an extinction as high as 

 20° were observed, showing that a plagioclase somewhat more basic than 

 albite is also occasionally present m very small amount. The microcline 

 presents its usual characters and is frequently intergrown with albite, 

 foraiing microperthite. The nepheline is in the form of large individuals 

 similar in shape and dimensions to those of the albite. Smaller in- 

 dividuals of it are sometimes seen to be included in the albite, while, 

 in other cases, it includes individuals of albite. It is very fresh and 

 free from alteration products. The lepidomelane is the same dark brown 

 highly pleochroic variety of biotite which occurs in the transitional rock 

 lying between the granite and the nepheline syenite (p. 32) and has the 

 forai of short laths. A lighter coloured mica is also present in, smaller 

 amount. The calcite occurs in large single individuals, often of a 

 rounded form, sometimes enclosed in the feldspars, nepheline or lepi- 

 domelane, but usually lying between the other constituents. The en- 

 closing minerals show no signs of alteration and the calcite shows no 

 signs of secondary origin. The magnetite is in large sub-angular or 

 more or less rounded grains. There seems to be no definite order of 

 succession in the crystallization, seeing that the various minerals en- 

 close and penetrate one another. The lepidomelane, however, has a much 

 better form tlian ihe other constituents and would thus seem to have crys- 

 tallized earlier. 



An analysis of the biotite-bearing variety of this nepheline syenite 

 was made by M. F. Connor, B.Sc, and gave the following results: — 



SiOg 51.58 percent. 



TiO, .35 



ALOV. .. 19.40 



Fe,0, 4.26 



FeO 5.25 



MnO .20 " - 



CaO 3.64 



MgO .49 



K^O '4.23 



Na,0 7.49 



P,6, 15 



CO, 1.53 



H,0 1.02 



99.59 

 Sec. IV., 1907. 3. 



