I78 HOLLAND: CHARNOCKITE SERIES. 



linear disposition of the constituents coincides with the direction of 

 the exposed ridges as well as the coast line which runs a few degrees 

 east of north to west of south. The petrological characters of the 

 rock have been described on p, 146. 



On the slight grounds of its resemblance in mineral composition 

 to the coarse-grained quartz-felspar rocks associated with, and some- 

 times occurring as veins in, the charnockite of St. Thomas' Mount 

 and Pallavaram, I have referred this rock to the charnockite series 

 and have regarded the dirty white colours of its felspar as due to 

 decomposition. In another section of this paper (p, 197), I have 

 pointed out the differences between simple subaerial action (which 

 in the compact charnockite series appears to be very limited 

 in its effects) and the hydration, due possibly to submarine action, 

 which extends to greater depths through the rocks. It is more 

 likely that the low-lying rocks near the coast have been depressed 

 more often and to greater depths than the higher portions of the 

 hills and the rocks further inland, and if there really is the difference 

 between the two kinds of decomposition — subaerial and submarine — ■ 

 such as I have imagined, it is not unnatural to expect that the low- 

 lying crystalline rocks near the coast will be found to have lost the 

 freshness which is so characteristic of the charnockite series in the 

 Shevaroy and Nilgiri Hills for instance. Although the narrow fringes 

 of marine beds lying near the east coast of Madras cover only a part 

 of the land which has in past ages been depressed below the sea-level, 

 the absence of all traces of marine deposits further inland justifies 

 the conclusion that subaerial denudation has proceeded uninterrupt- 

 edly for many geological ages on the high lands of the Madras 

 Presidency. 



South Arcot District. 



The only detailed account of the distribution of the char- 

 nockite series in South Arcot District is due to Dr, H. Warth, who 

 surveyed a portion of the district during the field-season 1894-95. 

 Unfortunately no opportunity occurred for tracing out the relations 



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