SUMMARY. 215 



rocks, in fact, have previously been regarded, on account of their 

 foliation, as normal members of the Archaean crystalline schists. 

 Their chemical, mineralogical and structural peculiarities are, how- 

 ever, in agreement with the general type of elaeolite^syenite of 

 undoubtedly eruptive origin. 



But besides their general agreement in average composition 

 and petrological characters, the family of elaeolite- 



Presence of graphite. 



syenites have a curious way of presenting some 

 new and strange feature peculiar to each occurrence discovered. In 

 this case the presence of graphite so evenly distributed through the 

 rock appears to be a feature quite new to the elaeolite-syenites, and for 

 that matter, new to normal eruptive rocks generally. The presence 

 of graphite in certain members of the crystalline schists is some- 

 times quoted as part of the evidence pointing to their sedimentary 

 origin ; but when it is so accompanied by nearly 15 per cent, of alkalies 

 in a rock whose structures so perfectly imitate those of unequi- 

 vocal eruptive elaeolite-syenites, the graphite must be considered to 

 be as much an igneous mineral as the eldeolite itself. The graphite 

 in these rocks shows the phenomenon of "sprouting" regarded by 

 Moissan as characteristic of graphite crystallized from fusion. 



The remarkable freshness of the elaeolite, as well as of all the 

 Freshness of South Indian other constituents of these rocks, is not incon- 

 " sistent with their probably great age. Indeed, 



the preservation from hydration of such a delicate mineral as elaeolite 

 is only in agreement with the remarkable freshness of the equally 

 susceptible olivine, which has been found unaltered in other very 

 ancient rocks in South India. An explanation of this freedom from 

 hydration has been offered by the Author elsewhere (Rec. Geol. Surv. 

 /«</., XXX, 40; Report Brit. Assoc, 1898,868; GtoL Mag., VI, 

 * 8 99> 540). 



The whole of these rocks are regarded as genetic relatives, formed 

 by the differentiation of a highly aluminous and alkaline magma. 

 The petrologically different types belong to one petrographical 



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