igo HOLLAND: CHARNOCKITE SERIES. 



highly garnetifcrous as well as graphitic ; it is along this band of 

 peculiar rocks that the charnockite series march with the Mercara 

 group of gneisses and schists, and the phenomena here displayed 

 are regarded by Dr. Walker and myself to be due to contact 

 metamorphism, though it is difficult to decide the exact boundary 

 line between the two great formations and so distinguish endogenous 

 from exogenous products. 



The chief feature of interest in connection with the eastern 

 occurrence in Coorg is the frequent dis- 



Dykes • 



play of narrow bands of basic charnockites 

 in the biotite-gneiss. Careful examination of these has 



revealed the curious fact that they all possess fine-grained 

 basic and hornblendic selvages which are almost certainly the 

 result of chilling at the margins. These bands must, therefore, 

 be regarded as dykes intruded into the older biotite-gneiss. They 

 vary very greatly in width, sometimes being merely a few inches 

 in thickness and at other times swelling out to large masses 

 Several of these are very clearly exposed in the bed of the Cauvery 

 at Fraserpet (see plate XIII), In their mineral composition and 

 structure they display the essential features which characterise 

 the charnockite series and like them often contain garnets (Nos. 12*395 

 to I2'405). Their association with larger masses of the more 

 normal types leaves little doubt about the conclusion that these 

 dykes are true members of the charnockite series and under the 

 circumstances must be regarded as strong evidence in favour of 

 the Conclusion that these rocks are igneous in origin and intrusive 

 in their relations to the older gneisses. 



Madura and Tinnevelli. 

 In the Palni Hills we have a mass of the charnockite series, 

 as large as that of the Nilgiris. The Palni 



Palm Hills, ? 



mass is 54 miles long trom east to west and 

 15 miles broad; including Anjinad, it covers 798 square miles. 

 The plateau is at an average elevation of 7,000 feet above the sea, 

 and is characterized by scenery similar to that on the Nilgiris. 

 In all the hill masses composed of the charnockite series the gentle 



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