﻿132 PROF. F. DAWSON ADAMS ON THE [May I908, 



SiOa 



I. 



Per cent. 

 73-33 



11. 



Per cent, 

 76-99 



TiOs 



017 





AloO, 



13-55 



12-45 



Ve 0' 



0-58 



1-03 



FeO 



MnO 



CaO 



1-63 



004 



1-66 



0-45 



312 



0-49 

 tr. 

 0-98 

 0-21 

 4-29 



Na,0 



erf, 



H,0 



501 



l['''['^[' [''["'. 045 



3-46 



none. 



0-26 





99-89 





Totals 



100-16 



I = Gneiss, Township of Methuen, Lot 17, Eauge V (M. F. Connor, 

 analyst). 

 11= Gneiss, Township of Livingstone, Lot 10, Eange V (N. Norton-Evans, 

 analyst). 



No. I is seen under the microscope to consist of microcline and 

 plagioclase, with small amounts of quartz and of an untwinned 

 felspar, as well as a very subordinate amount of biotite and 

 hornblende. 



It is impossible in the case of this analysis to calculate the exact 

 proportions of the iron-magnesia constituents which are present, on 

 account of the fact that the exact composition of these minerals 

 is not known. The ' norm/ however, is given below. By this is 

 meant the calculation of the analysis into the form of certain 

 standard minerals, showing the mineralogical composition of a rock 

 into which such a magma might crystallize under slightly-different 

 conditions.^ The norm represents in this case very nearly the 

 true percentage of the various minerals present, although diopside 

 and hypersthene are calculated as present, which are represented 

 by other combinations in the actual rock. It is as follows : — 



Orthoclase 18-35 



Albite 42-44 



Anorthite 5-28 



Quartz 2772 



Diopside 2-57 



Hypersthene 1*92 



Magnetite 0-93 



Ilmenite 0-30 



Total 99-51 



In this rock the albite and anorthite shown in the analysis are 

 combined, in the form of an acid plagioclase which is present in a 



1 See ' Quantitative Classification of Igneous Koeks ' by Whitman Cross, 

 J, P. Iddings, L. V. Pirsson, & H. S. Washington. University of Chicago Press, 

 1903, p. 147. 



