CLASSIFICATION OF THE ROCKS. 121 



basic segregations are found ; these are generally more hornblendic 

 and finer in grain (Nos. 11*910, 11*911) than the ordinary rock in 

 which they appear to be included. At their margins these bodies are 

 found on careful microscopic examination to pass gradually, though 

 rapidly, into the general main mass of the rock. They correspond 

 exactly to the basic Schlieren which are so commonly found in granites, 

 syenites and other plutonic igneous masses, and are considered to be 

 portions of the magma which have consolidated in advance of the 

 main mass. Their fine-grained structure, basic composition and 

 hornblendic character are all features generally displayed by the 

 border facies of these rocks. In Coorg, where dykes of the charnoc- 

 kite series have recently been discovered, these special points of 

 character distinguish the selvages from the central portions of the 

 dykes. Sometimes the basic, early-formed Schlieren become broken 

 up and the pieces cemented by the subsequently consolidated, more 

 acid, rock, producing a sort of primary eruptive breccia or protoclastic 

 structure • numerous cases of this kind are to be seen in the Shevaroy 

 hills. 1 



Important light is thrown on the nature of the charnockite 



series by a section exposed near the Namakkal 



SSSJ cSlmSr road, 3* miles south of Salem. The quarry in 



which this section is exposed occurs at the 

 junction of the charnockite series which forms the main-mass of the 

 Jarugamalais, lying to the east, with the old biotite-gneisses which 

 stretch away to the west and crop up at intervals in the well culti- 

 vated plain. On the freshly exposed rock-surface, tongues of the 

 charnockite series, proceeding from the direction of the great Jaruga 

 hill-mass, are seen to protrude into the biotite-gneiss, running ob- 

 liquely to the foliation planes of the latter. The charnockite is 

 slightly more basic than the average intermediate kind, having a 



1 For a fuller discussion of these structures see the Memoir on the Charnockite Series (Vol. 

 XXVIII, pt. 2). 



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