GEOLOGICAL RELATIONS AND ORIGIN. 175 



phenomenon of u sprouting " on heating after treatment with fuming 

 nitric acid, whilst he distinguishes the variety which does not 

 "sprout " as graphitite. According to Moissan 1 the former variety- 

 is produced by crystallization from fusion, whilst the non-sprouting 

 graphitite is formed by the metamorphism of amorphous carbon at 

 high temperatures. It is not known to what extent this generaliza- 

 tion may be extended, for the precise mode of origin of many of the 

 graphites examined by Luzi must be a matter of doubt. Moissan's 

 conclusion is satisfactory as far as the Sivamalai elaeolite-syenite is 

 concerned, for its graphite " sprouts " most distinctly. But I also 

 find this property to be displayed by the graphite of the crystalline 

 limestone of Sagyin in Burma, though I see no theoretical reason for 

 objecting to the suggestion that this limestone has been in a state 

 akin to fusion. Calcite is evidently a primary mineral in this elaeolite- 

 syenite and appears as such in other occurrences of this essentially 

 igneous rock. 



The balance of evidence is most distinctly in favour of consider- 

 Balance of evidence as in S the Sivamalai elaeolite-syenite to be eruptive 

 to origin. j n immediate origin: it presents the features 



generally displayed by plutonic masses, as well as the peculiar 

 characters of the occurrences of elaeolite-syenites which are known to 

 be eruptive. Judged by the test of chemical composition, which 

 Rosenbusch % has suggested as a means for distinguishing gneisses of 

 eruptive from gneisses of sedimentary origin, there should be no 

 hesitation in classing this rock with the chemically similar eruptive 

 elaeolite-syenites ; no sedimentary rock has ever been found with 

 such an abundance of alkalies as the Sivamalai rock shows. If 

 an eruptive origin then be ascribed to this rock, the presence of 

 graphite as a constant primary constituent adds another variety to 

 the remarkable group of elaeolite-syenites, of which almost every 



1 Comptes Rendus, CXXI, 538—540 and 540— 542, 1895. 



7 Zur Auffassung der chemischen Natur des Grundgebirges. Tschermak's 

 min. und petr. Mittheil., Volume XII (1891), p. 49. 



( 7 ) • 



