CLASSIFICATION OF THE ROCKS. 1 1 7 



their structure and the prevalence in them of hornblende, the hyper- 

 sthene which always accompanies and often quite replaces the horn- 

 blende not being recognised till the rocks were microscopically ex- 

 amined at a much later date. As early as 1864 King and Foote had 

 recognised this type of rock in other large mountain masses in South 

 India, and called attention to its existence as the typical form of 

 rock in the Nilgiri and Anaimalai hills. In later years it was iden- 

 tified at many other places in the south, and became distinguished by 

 Mr. Foote as belonging to the Salem division of the gneisses, being 

 considered to be younger than the granitoid type of Bellary and that of 

 the Baramahal division of the Salem district. Although the observa- 

 tions which I have made in the neighbourhood of Salem point to the 

 charnockite series ("Salem division of the gneisses ") being younger 

 than a biotite-gneiss in the same area, we have no evidence for con- 

 necting this biotite-gneiss with that of the Baramahal portion of 

 Salem district to the north, or with the granitoid gneiss of Bellary 

 district. The charnockite series have a long junction line with the 

 Baramahal. biotite-gneiss in the Salem district, but no attempt has 

 been made so far to work out the relations of the two rock groups 

 along this junction line. That the two are quite distinct in their 

 characters, and therefore almost certainly different in age and origin, 

 cannot be doubted ; but as to their relative ages we have so far no 

 direct evidence. Biotite-gneisses are altogether too common to per- 

 mit the assumption that the biotite-gneiss near Salem belongs to the 

 same formation as that of the Baramahal in North Salem district ; in- 

 deed the two present differences which indicate that they are distinct. 

 The results of the observations made near Salem have, therefore, 

 no necessary bearing on the question of the relations between the 

 charnockite series and its more northerly neighbour, the granitoid 

 gneiss of the highland taluks (Baramahal) and the plateau of Mysore. 



The <( intermediate " varieties. 

 The rocks exposed in the neighbourhood of Salem include a 



( 15 ) 



