APPENDIX, 77 



The cleanest specimens are composed of interlocking granules of quartz, gene- 

 rally very small, but sometimes large and irregular, with elongation in the direction 

 of the banding. The cystals do not show independent inclusions ; but small needles 

 and plates of black and brown minerals are embedded in the quartz, striking 

 irregularly across the boundaries of adjacent cystals. Cloudy bands of very minute 

 inclusions also traverse the rock. 



The iron-ore is generally concentrated along bands which are frequently 

 crumpled. The grains are often isometric in outline and consist of a mixture of 

 magnetite and hematite as in the case of the more coarsely crystallized quartz-iron- 

 ore rocks associated with the crystalline rocks further south in the Madras Presi- 

 dency. Chemical examination of a specimen (No. — .Jj from near the base of the 

 Dharwars on the eastern margin of g the Kolar gold-field gave the following 

 result : — 



11*67 percent. 



3 6 '°3 



34-27 „ and 



37"6i „ 



io'o6 „ 



Ferrous oxide (FeO) 

 Ferric oxide (Fe 2 O s ) . 



Equal to Iron (Fe) . 



Magnetite (FeO. Fe 2 3 ) 



Hematite (Fe 2 O g ) 



Plates and needles of a brown colour are associated in this rock with colourless 

 needles of a mineral undetermined. The mineral grunerite, so common in the 

 quartz-iron-ore rocks in the Madras Presidency (Salem district, for instance) 

 has not been identified in these Kolar rocks. 



Mr. Foote especially refers to these rocks as hematitic quartzites, and so dis- 

 tinguishes them from the magnetic iron-ore beds amongst the gneisses further 

 south in the Carnatic. 1 The distinction is not, however, very satisfactory, being 

 merely a matter of degree and that not always a noticeable one. In a paper just 

 published, I have pointed out that the so-called magnetic ore-beds occurring 

 amongst the gneisses of Salem, Malabar, and other districts, the magnetite is always 

 accompanied by a large proportion of hematite, sometimes exceeding the magnetite 

 in quantity, and on an average forming about 46 per cent, of the total ore. In the 

 one specimen from the Dharwars of Kolar the magnetite, it is seen, greatly exceeds 

 the hematite in quantity, and the relative abundance of the two ores is thus the 

 reverse of what would be expected if the distinction drawn by Mr. Foote were 

 universal. 2 



/. Hornblende schists. 



The hornblende schists are generally tough, dark greenish-grey rocks, with 

 a specific gravity Z'°2>~3'°9- They show a distinctly foliated structure in hand- 

 specimen, and this is sometimes accentuated by banding with coarse-grained 

 pyroxene layers or thin lenticles of brown mica. Effervescence with acid re- 

 veals the presence of calcite in nearly every specimen, sometimes in thin films along 

 joint planes, sometimes as distinct crystals, especially in the pyroxenic bands. A 



< \ Foote. Rec. Geol. Surv. Ind., Vol. XV, p. 202. 



2 Cf. Holland, "Geology of the neighbourhood of Salem." Mem; -Geol. Surv. Ind., : 

 Vol. XXX, p. 112. ... 



