REPORT OF THE CHIEF ASTRONOMER 



305 



SESSIONAL PAPER No. 25a 



in other parts; these two feldspar varieties are here clearly transitional into 

 €aeh other. The extinction-angle of the soda-orthoclase is 10° 30' on (010), 

 showing- a high content of soda. Its double refraction is markedly low. It is 

 possible that some of this homogeneous feldspar is anorthoclase, but the extinct 

 tion of flakes cleaved parallel to (001) was found, in three cases, to be parallel 

 and thus corresponding to the monoclinic isomorphic mixture. The schilleriz- 

 ing effect, like the chemical composition, relates this feldspar to the dominant 

 feldspar of Brogger's original laurvikite. 



The alkaline feldspar often encloses poikilitically idiomorphic to sub- 

 idiomorphic plagioclase, which occurs always in relatively small crystals, 

 averaging about 0-5 mm. in length. These are commonly twinned according 

 to the Carlsbad and albite laws and are often irregularly zoned. The average 

 plagioclase is labradorite, near Ab 4 An... Moderate amounts of apatite and 

 magnetite are accessory, while very rare, interstitial grains of quartz are also 

 found. The structure is the hypidiomorphic-granular. The order of crystalliza- 

 tion appears to be: apatite and magnetite; augite; biotite; plagioclase; soda- 

 orthoclase (and microperthite) ; quartz. 



Mr. Connor's analysis of a fresh specimen (No. 671) gave the result: — • 



Analysis of Salmon River Monzonite. 



TiO 



1-32 



ALO, 



16-91 



Fe„O a : 



1-71 



FeO 



6-17 



MnO : 



•16 



MgO 



5-50 



CaO 



8-26 



SrO 



-08 



BaO 



.,23 



Na,0 



2-89 



K 2 



445 



H,0 at 110°C 



.14 



HoO above 110°C 



1-06 



P-0-, 



-91 







Sp.gr 



100-45 

 2-843 



The calculated norm is: 



Albite 









Olivine.. 



Ilmenite 



Magnetite 



Apatite 





Mol. 

 844 

 016 

 166 

 Oil 

 086 

 002 

 138 

 147 

 «01 

 001 

 047 

 047 



•006 



26-13 



16-77 



4-26 



20-02 



13-32 



11-19 



2-43 



2-55 



1-86 



1-20 



99-73 



25a — vol. ii — 20 



