l82 HOLLAND: SIVAMALA1 SERIES. 



The molecules of bases are thus 55*6 per cent, of those of silica, 

 and the acidity co-efficient (a) = r8i, whilst the ratio of the alkalies 

 to other bases is 3 : 1. 



Loewinson-Lessing gives for 12 elaeolite-syenites :— 



SiO, 



A1 2 3 



Fe 2 3 



FeO 



CaO 



MgO 



K 2 



Na a O 



$ 0-231 



0928 



0*214' 



o'oi; 



0*020 ") 



0031 > 0*063 

 COI2 j } 0*268 



0*064 ■) , m 



o'i 4 i) ° 2 ° 5 



Molecules of bases amount to 54 per cent, of the silica; acidity 

 co-efficient (a) = 1*91 ; ratio of alkalies to protoxides is 3*2 : 1. 



By determining the proportion of the rock soluble in hydro- 

 chloric acid, the approximate proportion which the elaeolite bears to 

 the other constituents has been calculated. The powder was treated 

 with hydrochloric acid, and the liquid evaporated to dryness in order 

 to reduce the gelatinous silicic acid to insoluble silica. The soluble 

 salts were then removed in the ordinary way; the residue so obtained 

 was composed of the insoluble constituents of the rock, plus the 

 silica of the decomposed elaeolite, and amounted to 77*4 per cent, 

 of the rock taken. As the only two minerals in the rock appreci- 

 ably soluble in hydrochloric acid are the elaeolite and the magnetite, 

 the iron in the solution must have been practically all derived from 

 the magnetite. Deducting the iron, which amounted to 3*63 per 

 cent, (calculated as Fe 3 4 ), from the dissolved materials, the 

 remainder, 18*97, must be due to the alumina and alkalies of the 

 elaeolite. Knowing from the separate analysis of the elaeolite that 

 its bases constitute 56 per cent, of the mineral, 18*97 P er cent - of 

 bases would be equivalent to nearly 34 per cent, of the mineral in 

 the rock. These estimates, 34 per cent, of elaeolite and 3*63 per 

 cent, of magnetite, are probably close approximations to the com- 

 position of the ordinary grey form of elaeolite-syenite in Sivamalai. 

 The felspars are too variable in their composition to permit of the 

 ( 14 ) 



