

CORUNDUM-SYENITE. 203 



to small quantities of secondary minerals, and calculating the 

 molecular ratios, we obtain :— 



SiOo . . i'o66 



A1,0 3 

 Fe 2 O s 



CaO 

 K a O 

 Na a O 



SSo?}' 0-216 R f O,. 



0*004} 



0033 > . 0*200 RO. 



0*167 J 



The ratio of K 2 : Na 2 0= 1 : 5, and of A1 3 3 to the other bases, 

 a little in excess of 1 : 1 on account of the small quantities of mus- 

 covite and kaolin, which are of secondary orgin. As a magma for 

 the solution of alumina and subsequent separation of corundum this 

 rock conforms perfectly to Morozewicz's law (see p. 39) : soda pre- 

 dominates amongst the alkalies, which makes it a good solvent for 

 alumina, whilst the protoxides, being already satisfied with alumina, 

 any excess would separate in the free condition. Minute quantities 

 of BeO and ZnO have used up a corresponding quantitity of AI 2 3 

 in the form of accessory chrysoberyl and automolite respectively. 

 These have been excluded from the analysis. 



The felspar-rock has been referred to by Middlemiss as a coarse- 

 grained, pink granite (Rec. GeoL Surv., Ind., XXIX, 47 and 48) ; 

 but quartz is generally absent and when present is in extremely 

 small quantities ; it can only be regarded as an accidental and local 

 accessory, being altogether difficult to find. In the fields around, 

 however, large quantities of quartz fragments are found, probably 

 derived from the more acid pegmatites and quartz veins which also 

 occur in this neighbourhood. 



Not more than a couple of miles or so from the western 

 end of the row of elaeolite-syenite hillocks occur large quanti- 

 ties of graphic granite cutting through a mica-gneiss or schist; 

 it is from one of the drusy veins in this rock that the aqua-marines 

 were obtained by Heath early in the century, and some of the 

 colourless quartz was recently, and possibly still is, carried to Trichino- 

 poly and Tanjore for the manufacture of the so-called " Vallum 



( 35 ) 



