s?*fH 



194 1 HJLLAND: SIVAMALA1 SERIES. 



An unaltered eruptive rock, on the other hand, usually shows a fixed 

 order of succession amongst its constituents. Exactly why there 

 should be this difference between simple eruptives and the old 

 crystalline rocks has not been explained ; but the evidence of these 

 elaeolite-syenites and of the pyroxene-granulites in South India 

 tends, in my opinion, to show that the contradictions and apparent 

 oscillations in the order of crystallization are due to disturbances 

 during consolidation, just as, according to Professor Judd, the ophitic 

 intergrowths of augite and plagioclase give rise to a granulitic struc- 

 ture when the basic rocks are moved during the process of crystalli- 

 zation. 



i (d). Variety containing hornblende and calcite, but without 



graphite. 



This type contrasts with those described above in the follow- 

 ing points : — 



(1) There is almost a complete absence of opaque iron-ores, 



which in the varieties described above are much more 

 abundant than is usually the case with the elaeolite- 

 syenites. 



(2) Biotite occurs only in very small quantity, being replaced 



by a barkevikitic hornblende, which is gathered into 

 granular groups measuring half an inch or more across, 

 and giving the rock a mottled appearance in hand-speci- 

 men. 



(3) Calcite is present in granular crystals, which are more 



particularly abundant within the dark hornblendic patches, 

 although isolated crystals occur also in the felspathic 

 groundmass. 



(4) Elseolite is much less abundant than in the grey rock 



(!#, b and c). It occurs in small crystals which tend to 

 aggregate, like the calcite, within the hornblendic areas. 



( 26 ) 



