J. K. Coomarasicdmy — The Balangoda Group. 419 



averaging perhaps a hundred yards in width, runs, parallel to the 

 Charnockite foliation-strike, along the trough-like strike valley 

 of the Massena Oya, in which the main part of the estate is found. 

 The rock occurs in enormous masses, both in situ and in great 

 boulders, amongst which the Massena Oya finds its way. Two rows 

 of curiously weathered masses stand out of the swamp below the 

 bungalow ; good specimens very rich in zircon can be collected 

 here. The rock usually shows no trace of foliation in small 

 specimens; but foliation (vertical, with strike about 15° N. of W.) 

 is evident in an exposure in situ near the middle of the estate, near 

 the '■ lines.' 



The rock consists essentially of quartz, felspar, and biotite, with 

 zircon and ilmenite as characteristic accessory minerals, and apatite 

 as a microscopic constituent. The content of zircon varies greatly 

 from specimens in which a crystal can hardly be found to others 



i M B U LPE 



S A 



alutnuwera 



J^^^ifiatC 



Fig. 1. — Eougli sketch-map of zircon granites near Denagama Oya bridge, near 

 Balangoda, Sab, Ceylon, x x x zircon granites ; t zircon granites well 

 foliated. Scale, 5 inches = 1| niUes. 



in which it forms a noteworthy proportion of the rock. The zircon 

 occurs in moderately good, idiomorphic, stumpy, prismatic crystals, 

 generally terminated, the forms m (110), a (100), f (HI), e (101) 

 being certainly present ; the colour is hair-brown, often quite pale ; 

 in thin section no colour is seen ; the longest individuals exceed 

 |- inch in length, but most are somewhat smaller. The rock itself 

 is relatively fine-grained, the quartz and felspars rarely exceeding 

 in diameter the length of the longest zircons. The felspars include 

 orthoclase (sometimes microperthitic) and an acid plagioclase with 

 s.g. near to that of orthoclase. The biotite occurs in ragged cr^'stals, 

 macroscopically nearly black, but brown in thin section, and with 

 pleochroism from warm brown to pale straw colour. Ilmenite is 

 common, occasionally moulding the zircons, and generally partly 

 altered to ' leucoxene.' Apatite is fairly abundant in six-sided 

 terminated prisms about -^o" inch in length. The general structure 

 is hypidiomorphic, only the zircon and apatite occurring in well- 

 developed crystals. 



