Vol. 57.] OF SOUTH-CENTKAL CEYLON. 209 



frequently biotite. Irregular grains of quartz are common. There 

 can be, I think, no doubt that these rocks are closely related to 

 those of § II, p. 202. 



Mr. T. H. Holland,^ in a most valuable memoir, describes 

 ^ a group of Archaean Hypersthenic Rocks in Peninsular India ' under 

 the name of the Charnockite Series, and states that members of it 

 occur in Ceylon. Home stress is laid by Mr. Holland on the presence 

 of the rhombic pyroxene. So far as my work goes, it tends to 

 show that hypersthene is not distinctive of the Ceylon rocks. I 

 have not, in fact, found the indubitable mineral at all (though 

 it has been recorded by Mr, A. K. Coomara-Swamy), but a mono- 

 clinic pyroxene with the pleochroism of hypersthene does occur. 



, The preceding observations show that the series of igneous rocks 

 studied are closely related one to the other, and have arisen through 

 the variation of a single magma. This variation, in places, has 

 resulted in a well-marked differentiation into acid and basic parts 

 which, by subsequent intermingling, have produced a banded gneiss. 

 Further, the evidence brought forward indicates that these rocks are 

 younger than the crystalline limestone and are intrusive into it. 



; In conclusion, I wish to express my indebtedness to Prof. Bonney, 

 D.Sc, F.R.S., for valuable suggestions and help during the pre- 

 paration of this paper. 



Discussion. 



Dr. J. AV. Evans said he believed that the granulites described by 

 the Author appeared, like those of Southern India, to fall into two 

 classes: the hypersthene-granulites, grouped by Mr. T. H. Holland in 

 the Charnockite Series, which were usually comparatively massive 

 rocks ; and highly-banded granulites, in which hypersthene was 

 absent or played a subordinate part. The latter were well seen in 

 the auriferous beds of the Kempinkote Mine, where they might be 

 considered as quartz-diorites with a granulite-structure. 



Gen. McMahon said that the President had alluded to the pro- 

 bability that the Ceylon rocks described in the paper under discus- 

 sion are connected with the Charnockite Series of Peninsular India, 

 and he understood that the Author considered the banding and 

 foliation observable in the Ceylon rocks to be due to causes similar 

 to those relied on by Mr. Holland : namely, the flow of the magma 

 during the process of consolidation. 



Mr. A. K. Coomara-Swamy said that he regarded the conspicuous 

 mineral-banding seen in manj^ Ceylon rocks as rejiresenting a sort 

 of fluxional structure acquired at the time of consolidation. The 

 rocks seemed to be practically unaffected by earth-movements of a 

 shearing or crushing character, but exhibited structures which are 

 probably original. 



1 Mem. Geo]. Surv. India, vol. xxviii (1900) p. 119. 



