REPORT OF THE CHIEF ASTR0X031ER 451 



SESSIONAL PAPER No. 25a 



The mode (Eosiwal method) is approximately: — 



Microperthite 1 



Microcline }• 36-3 



Soda orthoclase J 



Augite 36-5 



Biotite.. 11-0 



Melanite.. , 9-5 



Nephelite 5-4 



Apatite 1-0 



Magnetite and titanite -3 



100-0 



In the Norm classification the rock enters the sodipotassic subrang, boro- 

 lanose, of the domalkalic rang, essexase, in the dosalane order, norgare. 



According to the principles of the older classification the nearest relatives 

 to this rock are found in the malignites of Ontario, as described by Lawson 

 (see Table XXV ill, Cols. 5, 6 and 7). This Krager mountain rock differs from 

 the Ontario types chiefly in the fact that here potash greatly predominates over 

 the soda. Though in this respect the rock is an extreme member of the group 

 named by Lawson, it is, apparently, best classified as an augite-biotite malignite. 



Femic Nephelite Syenite.' — The second analyzed specimen was collected near 

 the contact with the Kruger Mountain schists at a point about 1,000 yards 

 northwest of the locality where the first specimen was found. This second rock 

 is a bluish-gray, medium-grained, somewhat porphyritic type. The phenocrysts 

 are tabular crystals of microperthite, reaching 1 cm. or more in length. Qualita- 

 tively the mineralogical composition is like that of the specimen just described. 

 Here, however, the fernic constituents are decidedly less abundant, while the 

 feldspars and nephelite have notably increased. The order of crystallization 

 and the decomposition-products are, respectively, the same as in the first speci- 

 men. In the thin section of the second specimen it was observed that the garnet 

 and biotite interpenetrate so intimately as to suggest a primary origin for the 

 former, though decisive proof of that has not been found. Like the first speci- 

 men, this one has been somewhat crushed, so that a metamorphic origin of the 

 garnet is quite possible. The rock powder gelatinized strongly on heating with 

 acid, showing that nephelite is abundant. Optical tests seemed to show that 

 some free albite here accompanies the other feldspars. 



Professor Dittrich's analysis ("specimen ISTo. 1110) gave : — - 



Analysis of femic nephelite syenite, Kruger alkaline body. 



Mol. 



SiOo 52.53 -875 



TiOo -07 -001 



ALA 19-05 -186 



Fe„0, 4-77 -030 



FeO 2-10 -029 



MnO -13 -001 



MgO 199 -050 



BaO -09 -001 



CaO 5-75 -103 



SrO .19 -002 



25a— vol. ii— 29£ 



