188 OCCUERENCE OP COEUl^DFM AS A CONTACT-MINERAL. [MayipOI, 



amount of felspar found in the inclusions we may well suppose 

 that some has been derived from the surrounding granite, for the 

 metamorphism has evidently been very intense. Doubtless the 

 inclusions were never in a state of igneous fusion ; but there has 

 been a sufficient amount of molecular freedom to admit of the 

 formation of comparatively large, sharp-edged crystals of corundum,, 

 without many inclusions. The original sedimentary rock was 

 probably poor in silica. 



The presence of corundum in the enclosing granite has not been 

 noticed ; it would be interesting to examine the decayed rock, 

 especially in the neighbourhood of the inclusions, in order to see 

 whether any corrosion thereof has led to the presence of corundum 

 in the granite.^ 



It is interesting, to compare this occurrence of corundum as an 

 undoubted contactrmineral in included fragments, with those 

 described in Southern India by Mr. C. S. Middlemiss,^ which are 

 supposed to result from the metamorphism of foreign inclusions. 



In conclusion, I have great pleasure in expressing my in- 

 debtedness to Prof. Barrois, who not only very kindly directed me 

 to the Pont Paul locality, but also gave me full permission to 

 describe the rocks. I have also to thank Prof. Bonney for allowing 

 me to examine his slides of other altered rocks from Morlaix. 



Discussion. 



Mr. H. D. Oldham remarked that, in Southern India, more than 

 one of the known occurrences of corundum had been recognized as 

 being in the marginal portion of an intrusive mass. In one instance 

 a direct causal connection appeared to have been established by 

 Mr. T. H. Holland. The corundum of Sivamalai occurred in a 

 coarse-grained felspar-rock intrusive in an elseolite-syenite, by 

 whose fusion an excess of alumina seems to have been introduced 

 into the intrusive rock. On the subsequent solidification of the last- 

 named the excess of alumina crystallized out as corundum. 



Mr. Parkinson called attention to a specimen on the table from 

 one of the ellipsoidal masses found in the Charnockite Series of the 

 Salem District (Madras Presidency). The mode of occurrence of 

 these lenticles and the large amount of corundum that they contain 

 make it extremely probable, according to the published accounts 

 of the district, that they are altered inclusions of some foreign rock. 

 He thought the specimen of interest in connection with the Author's- 

 paper. 



^ Compare K. Busz, ' On the Occurrence of Corundum produced by Contact- 

 Metamorphisin on Dartmoor ' Greol. Mag, 1896, p. 492. 



'■^ ' Preliminary Notes on some Corundum Localities in the Salem & Coim- 

 batore Districts' Eec. Greol. Surv. India, toI. xxix (1896) pp. 40-46; see 

 also T. H. Holland, ' Corundum ' pt. i of ' Economic Geology ' in the reissue of 

 the ' Manual of the Geology of India ' Calcutta, 1898, pp. 18 & 39-43, and Mem. 

 Geol. Surv. India, vol. xxyiii (1900) ' The Charnockite Series ' pp. 183 & 234. 



