192 jR. A. Daly — Secondary Origin of Certain Granites. 



Table II. 



Showing the weight percentages of minerals as determined by the Rosiwal 



method.* 

 1. 2. 3. 4. 5. 6. 7. 



Hornblende 58'7 54-8 429 49'4 .... ... _._ 



Biotite -9 ... 6*6 22'0 8'9 22*0 15*2 



nStV^ } ^ ^ 



Andesine, Ab 4 An 3 18*5 16'5 



Oligoclase, Ab^Ai^. _. ... ... 1*5 1'5 1*0 



Soda-bearingortho- J g .. ___ 24 . g ^ ^ 



Microperthite . . - ... 3*9 



Quartz 4-0 6*3 22*8 11'7 57*1 46'0 41'6 



Muscovite _ ... .._ _ 3*2 .... 4-6 



Apatite -2 ... ... -3 ... '5 -2 



Titanite 1-4 2*0 37 ... ... ___ .... 



Magnetite ... *3 ... ... 1*9 "5 1-0 



Chlorite ... 11-0 ... . . _._ ... ... 



Calcite ... .._ ... ... 2 5 -4 ... 



Total is 100 in each case. 



1. Normal unacidified gabbro from sill about eleven miles east 

 of the Moyie sill. 



Nos. 2 to 7 inclusive are types from the Moyie sill, specimens 

 taken thus : 



2. Thirty feet from lower contact. 



3. Two hundred feet from lower contact. 



4. Two hundred feet from upper contact. 



5. Fifty feet from upper contact. 



6. Forty feet from upper contact. 



7. Fifteen feet from upper contact. 



Table II was constructed by the use of the Rosiwal method 

 for the determination of the relative quantities of the different 

 constituents. The values are only approximate, owing to the 

 difficulties of exact measurement and identification of the min- 

 eral grains. No account was taken of the sometimes abundant 

 grains of epidote, occasional grains of calcite (measured in one 

 instance), and often rather abundant scales of kaolin which 

 occur in the slides. These minerals are products of the altera- 

 tion of the feldspars, that alteration affording another diffi- 

 culty in using the Rosiwal method for this suite of rocks. The 

 proportions of the micas are probably too high on account of 

 their not being even approximately equidimensional. Though 

 these rocks do not lend themselves to a very satisfactory 

 employment of the method, and though the table cannot be 

 considered as accurate, the strong contrasts between the acid 

 and basic phases of the sill are clearly evident. 



*Verh. Wien. Geol. Eeichs-Anst., vol. xxxii, 1898, pp. 143 ff. 



