80 HATCH : THE KOLAR GOLD-FIELD. 



streak thins down from half an inch to a mere film, and cuts obliquely across the foliation 

 planes of the quartz-iron-ore fragment. 



(3) Mica schist (brown mica) with band of cleaner granular quartz ( ? vein quartz ), both 

 types containing calcite. 



(4) Quartz-iron-ore rock, very fine-grained but comparatively rich in iron-ore, cemented 

 along a sharp junction line with a quartzose hornblendic schist, with a little brown mica and 

 calcite, but without recognisable felspar. 



(5) Quartz-felspar rock, comparatively coarse in grain and with much calcite in irregular, 

 ragged crystals, joined, with a ragged ill-defined junction line, to mica schist, which is about 

 \ inch thick and passes on the other side into a granular quartz rock with a little opaque black 

 iron-ore. 



(6) Fragment of comparatively coarse granite-gneiss containing sphene and apatite like 

 the ordinary granite-gneiss, but with signs of considerable alteration with formation of calcite, 

 etc. This is joined, with a fairly clean junction line, to a schist composed largely of brown- 

 green mica, much opaque black iron-ore, quartz, sphene, and epidote. 



(7) A schist composing apparently most of the material which in hand-specimen looks 

 like the matrix holding the " pebbles." In this rock a greenish-brown mica predominates over 

 blue-green hornblende, and the rock contains much epidote anJ quartz ; opaque black ores 

 being comparatively sparse and in well defined granules. The junction between this and the 

 granite-gneiss" pebble " is never sharp and is apparently a zone of intergrowth and reaction. 



The above description shows what a great variety of rocks are represented in 

 one large specimen, and I am inclined to regard this pseudo-conglomerate as the 

 result of the deformation of a Dharwar schist into which granitic material has 

 intruded, and would then look upon the variations in the schist and the so-called 

 granite-gneiss pebbles as the result of reaction under pressure. The quartz- 

 iron-ore rock fragments have preserved their individuality more completely than 

 any of the other types. 



(3) POST-DHARWAR DIABASE DYKES. 



The basic dykes cutting the Dharwars, and not themselves disturbed by subse- 

 quent earth movements, belong to the diabase (augite-plagioclase) class, and, like 

 many others of the same type traversing the crystalline schists of South India, 

 generally contain small quantities of micropegmatite. These rocks were described 

 in detail by me in 1897, 1 and the Kolar specimens do not differ essentially from 

 those previously described under Cole's term " augite-diorite." These rocks are 

 generally composed of a pale pyroxene (augite predominating), a pligioclase 

 felspar, near labradorite in composition, a small quantity of micropegmatite, and the 

 usual amount of iron-ore, which is generally titaniferous and sometimes pyritous. 

 As minerals of secondary origin, hornblende often fringes the augite crystals, 

 whilst biotite, chlorite, and secondary quartz are often found in, or in the neighbour- 

 hood of, the micropegmatitic patches. Epidote occurs also in much altered 

 specimens. 



The Kolar diabases vary in texture from the coarse-grained central portions of 

 the large north and south dyke, which cuts through the Mysore,Nundydroog, and 



> "On some Norite and associated basic dykes and lava-flows in Southern India." Rec. 

 Geol. Surv. Ind., Vol. XXX, p. 16, and "On Augite-diorites with micropegmatite in Southern 

 India." Quart. Journ. Geol. Soc., Vol. liii, p. 405. 



