The Monteregian Hills. 



227 



Albite 



Anorthite . . 

 Orthoclase . 

 Nepheline . . . 



Kaolin 



Pyroxene 

 Hornblende . 



Biotite 



Olivine 



Magnetite . . . 



Ilmenite 



Apatite . . 

 Water (hygr.) 



99.39 



Essexite 



Olivine-Essexite 



(Analysis 1) 



i Analysis 2) 



Mount Johnson 



Mount Johnson 



36.75 ) 

 20.23 66 45 



29.14 ) 



13.11 \ 54.79 



9 47) 



12.54 \ 



3.99 1 477 



.78) 4 ' ;/ 



»>*}n. 9 o 



6 29 



12.22 



7.05 



2.30 



2.04 



4.08 



none 



2.84 



5.68 | n -o 



3.85/ 9 " 53 



iS s «•« 



2.68 



2.59 



.58 



.85 



99.98 



In the case of No. 1 the percentage mineralogical com- 

 position given expresses exactly the chemical composition 

 of the rock, except that it requires 0.06 per cent, of FeO 

 in excess of that shown in the analysis. In No. 2 the 

 agreement is complete. 



The calculation further demonstrates that the plagi- 

 oclase in the case of No. 1 is a trifle more basic, and in the 

 case of No. 2 a little more acid, than Ab 2 An b which as 

 has been stated, is shown by the optical character and by 

 the specific gravity of the feldspar to represent its average 

 composition in these rocks. The amount of orthoclase 

 recognized in thin sections also appears as mentioned in 

 the description of the rock. The nepheline is in places 

 somewhat altered to a mineral resembling kaolin. The 

 small percentage of kaolin shown by the calculation has 

 therefore been added to the nepheline in extending th e 

 table. 



In order to fix the position of these rocks in the 

 excellent system of classification recently elaborated by 

 Messrs. Cross, Iddings, Pirsson, and Washington, and to 

 determine the name which should be given to these rocks, 

 if their precise character is to be designated, it is neces- 



