DESCRIPTION OF THE CHIEF TYPES. 135 



tatten durch Differentiation-processe'jn basischen Eruptivmagmata," 

 .. . ., ... and referred to the occurrence of a series of 



Norwegian granite with 



rhombic pyroxene. rocks at Ekersund in south-west Norway, which 



appear to strongly resemble those of Pallavaram. The three prin- 

 cipal types represented at Ekersund are, according to Vogt, (1) 

 labradorite rocks, resembling apparently the anorthosites of Canada, 

 (2) norites rich in hypersthene and biotite ; and (3) a granite 

 composed largely of potash-felspar and quartz with a rhombic 

 pyroxene approaching bronzite in composition, iron-ores in consider- 

 able quantities, and a small proportion of an acid plagioclase. 1 Such 

 a description applies exactly to the rock which is known to us in 

 South India as charnockite. But the resemblance of this special 

 type of rock to our charnockite becomes doubly interesting on 

 account of the similarity between the associates in both localities. 

 Although the norites and labradorite rocks differ from the granite 

 so widely in silica percentage, the whole group, according to Vogt, 

 belongs to one petrographical province in which all the members are 

 characterised by the presence of a rhombic pyroxene, and the rocks 

 show an unmistakeable consanguinity [Blutverwandschaft) which 

 leaves little doubt as to their derivation from an originally common 

 magma basin. Almost the same words were used in referring to the 

 relatives of charnockite as they are displayed in the neighbourhood 

 of Pallavaram. As remarked in a previous paragraph, the macro- 

 scopic characters of the various types so strikingly display the common 

 family characters of the group, that the differences which serve to 

 distinguish the varieties are often remarkably masked. 



At about the same time, therefore, and independently, Vogt 

 discovered in south-west Norway a granite resembling charnockite 

 both in its own composition and in the characters of its associates. 

 Vogt apparently (as well as myself) was under the impression that 

 rhombic pyroxene had not previously been recognised in a granite. 

 I am indebted to Professor Zirkel, however, for calling my attention 

 to the fact that Tornebohm found a rhombic pyroxene to be a 

 constituent of a granite in the neighbourhood of Roxen-See and 

 1 Zeitschr. fur prakt. Geol., 1893, p, 4, 



c ( 17 ) 



