APPENDIX. 75 



{Mem. Geol. Surv, Ltd., Vol. XXX, pt. 2), for instance, those which are foliated in 

 conformity with the hornblendic schists of the Dharwar type near Salem. 



The differences between these two specimens and the prevalent form of granite- 

 gneiss previously mentioned are not necessarily primary ; they may be due to mere 

 local secondary changes, but in view of the fact that two distinct biotite-gneisses 

 occur elsewhere in South India, the relationship of these two varieties should be 

 checked in the field. 



(2) DHARWARIAN. 



According to Mr. Foote's account of the Kolar gold-field, the Dharwar rocks 

 are arranged in the following order on the west side of the syncline : — 



f. Hornblendic schists with auriferous reefs. 



e. Chloritic schists. 



d. Quartzites and quartz-iron-ore rocks. 



c. Micaceous schist. 



b. Chloritic gneiss. 



a. Micaceous gneiss (resting on granitoid gneiss.) 

 The specimens representing stage a so completely agree in all essential 

 characters with the granitoid gneiss that I have separated them from the Dhar- 

 wars in this description. The rock appears to be only a highly crushed form of 

 granitoid gneiss, and quite different in characters to the mica schist of stage c. 

 Stages b and e are not represented in the specimens sent by Dr. Hatch. 



The auriferous quartz rocks are associated with the hornblende schists, and 

 were presumably formed after the latter. 



c. Mica Schist. 



Only one specimen of a true mica schist has been obtained, namely, from near 

 the base of the Dharvvars, north-west of Wallagamathaconda and near the 

 Champion Reef Mine pumping station. The specimen of micaceous and schistose 

 rock found associated with the mica schist contains much felspar and in all essen- 

 tial respects its composition agrees with that of a granitoid gneiss (q.v), merely 

 differing from the latter in being more highly crushed and altered. 



The mica schist (No. g ^ 4 ) is a well foliated rock in which silvery mica and 



a dark-greenish or dark- grey variety are associated. Microscopic examination 

 showed the colourless and the green pleochroic mica intimately interleaved. Scales 

 separated from the rock give sometimes a wide optic axial angle, as wide as that 

 of muscovite, and sometimes a confused figure which is due to the disturbed 

 condition of each crystal. An occasional stout prism of a colourless mineral, 

 probably apatite, with high refractive index and weak double refraction, appears 

 in thin section ; but the main mass of the rock is composed of mica and water- 

 clear quartz without any discoverable trace of felspar. 



A rock of this kind might very well be derived from a felspathic type by 

 metamorphism of the felspar into quartz and colourless mica, and it is not 

 impossible therefore that it is genetically related to No. J* 8 -, the highly foliated 



