8 4 



syenites, and, together with the high percentage of alumina 

 in the magma, probably explains the development of 

 corundum in them. 



The ratios of the molecular values of (CaO, K 2 0, Na 2 0) : 

 A1 2 3 : Si0 2 in the rock at present under consideration are 

 as follows: — 



•222 : 233 : 972 

 1 : 1 : 4-2 



The ratio of K 2 : Na 2 = 1:6 and alumina to the 

 bases is a little in excess of 1 : 1 . As a magma for the 

 solution of alumina and its complete separation as corun- 

 dum on crystallization, it is therefore in perfect agreement 

 with Morozewicz's law. Of the alkalies, soda largely pre- 

 dominates, this lending the necessary assistance in the 

 solution of the alumina. There is an excess of ferrous iron 

 and magnesia above what has been thought permissible 

 (0-05 per cent) by Morozewicz's law, but these amounts 

 have been necessary to assist in the formation of the 

 comparatively small quantities of magnetite and biotite 

 present in the rock. It is therefore evident that Moro- 

 zewicz's law, as remarked by Holland [7, p. 208] does not 

 represent the whole truth, for it might be expected, with 

 this excess of ferrous iron and magnesia, that spinel would 

 be formed in addition to the corundum. This mineral 

 was, however, not seen in the thin sections, nor was it 

 found in any of the outcrops in the vicinity where this 

 rock specimen was collected. 



The norm of the rock is as follows: — 



Quartz 1-26 



Orthoclase 7 • 23 



Albite 4I-9 2 



Anorthite 29-19 



Corundum 13 -46 



Hypersthene 4-12 



Magnetite 1-39 



Calcite -37 



98-94 

 Water -84 



99-78 



In calculating this norm from the chemical analysis, 

 there was, as shown, an excess of 1-26 per cent of silica 



