66 ROYAL SOCIETY OF CANADA 



formed in addition to the corundum. This mineral was, however, not 

 seen in the thin sections, nor was it found in any of the outcrops where 

 this rock specimen was collected. 



The norm of the rock is as follows : — 



Quartz 1.26 



Orthoclase.. 7.23 



Albite 41.92 



Anorthile 29.19 



Corundum 13.46 



Hypersthene 4.12 



Magnetite 1.39 



Calcite .37 



98.94 

 Water .84 



99.78 



In calculating this norm from the chemical analysis, there was as 

 shown an excess of 1.26 per cent of silica above that required and which 

 appears in the norm as quartz. By direct experiment it was subse- 

 quently shown that most, if not all, of this silica was derived from the 

 agate mortar and pestle which was used in grinding the sample. There 

 is no free silica or quartz shown in the thin sections, nor was any of this 

 mineral found in the separation of the rock by means of the heavy solu- 

 tion. 



The mode or actual mineralogical composition cannot be calculated 

 with certainty on account of the presence of the two micas and the 

 scapolite, the latter having about the same formula as the feldspar. The 

 corundum, magnetite and calcite are normative, i. e., they are present 

 essentially in the percentages given in the norm. From an inspection of 

 the slides the following would seem to be a very close approximation to 

 the mineralogical composition of the rock: — 



Andesine (near AbgAng) 72.00 



Nepheline 3.00 



Scapolite 2.00 



Corundum (by trial) 13.24 



Biotite 5.00 



Muscovite ' 3.00 



Magnetite 1.39 



Calcite .37 



100.00 



