■174 HOLLAND: SIVAMALAI SERIES. 



consolidation, With the very large number of instances now known 

 of foliation and even banding, of igneous rocks, no one probably 

 would consider this structure antagonistic to the evidences which 

 point to the eruptive origin of a rock. But when definite intrusion, 

 which is the main point of evidence, is wanting, and when a rock- 

 mass appears amongst the crystalline schists with conformable 

 foliation, it is only natural tfyat a conclusion in favour of its igneous 

 origin should be more than ordinarily criticised. And in the present 

 instance the presence of graphite, as an evenly disseminated con- 

 stituent, would naturally be regarded as a feature which corroborates 

 the evidence of the foliated structure and geological relations of the 

 rock in pointing to its membership with the crystalline schists. 



With regard to the graphite we are not, as is the case with 



the foliation structure, supplied with instances 

 Significance of graphite. . ... , 



of its occurrence in unequivocal igneous rocks. 



At the same time graphite has been found more than once under 

 circumstances, as for instance in some pegmatites, where its presence 

 could hardly be explained by metamorphism. The ultimate origin 

 of the graphite is, of course, not the point under discussion ; but its 

 occurrence in pig-iron and the Greenland iron-basalt shows that it 

 can be crystallized after simple fusion. In the case of the graphite 

 occurring in the pegmatites the crystals are moulded around by 

 quartz, which shows that it is not a product of sublimation, but is 

 a constituent older at least than the quartz. Similar evidence shows 

 that it is not a sublimated product in the Sivamalai elseolite-syenite : 

 it is older than the felspar and is not found merely in the coarse 

 veins, but scattered through the fine-grained rock, in the same way 

 as it is generally found in crystalline limestones. The question 

 of its origin, therefore, is confined to the two remaining explana- 

 tions, namely, crystallization from fusion or metamorphism of organic 

 carbon. 



Luzi 1 reserves the name graphite for the variety which shows the 



1 Berichte-d. deutsch. chem. Ges., XXIV, 4085—4095, 1891 ; XXV, 214—217, 

 1892 ; XXVI, 890—895, and 1412 — 1414, 1893. 



( 6 ) 



