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Vol. 66.] TOURMALINE-CORUNDUM ROCKS OF KINTA. 441 



(vii) 



Light-coloured rock with corundum only. 

 Localities various. 



(a) A very light-coloured rock. The base is fine-grained, and composed 

 apparently of silica and white mica. There is a little corundum showing no 

 definite structure. 



(b) The base of this rock is fine-grained and apparently siliceous. Blue 

 corundum occurs as veins (PI. XXX, fig. 3) and masses. There are numerous 

 round bodies like those already mentioned, but in some cases the material com- 

 posing them has been replaced by corundum. Fig. 4 (PI. XXX) shows a good 

 example of these bodies. The centre is of corundum darkened by black dust ; 

 the clear rim is of a finely crystalline material that may be micaceous but 

 cannot be determined. The unaltered bodies contain much pale-yellow opaque 

 matter, which is present throughout the rock. An accumulation of this in the 

 centre forms a nucleus for the bodies in some cases. 



(c) This rock resembles (v) a, and (v) b, but there is much carbon present 

 and a little corundum ; the latter, however, does not occur in the numerous 

 bodies, which are nearly all elongated, owing to a marked schistosity in the 

 rock. The bodies show concentric structure. There is a little pyrite. 



(d) This rock is coarser in grain than usual, and is distinctly rough to the 

 touch. It is weathered, and resembles sandstone. The section shows nothing 

 but discs of corundum, some of which are hollow in the centre, and yellow 

 opaque matter. A part of the specimen was fused with carbonate of soda, and 

 yielded 42'3 per cent, of corundum. It seems that something, probably mica, 

 was lost in making the slide. The corundum discs suggest in some cases round 

 bodies completely replaced by corundum, 



(e) A light-coloured rock with small, dark, blue-black nodules of varying size. 

 The base is siliceous, and full of minute micaceous flakes. Round bodies are 

 numerous, and show a faint concentric structure. In some cases they are 

 partly formed of corundum ; while one consists of a broad ring (in section) of 

 corundum, enclosing a fine mosaic of white mica. There are numerous opaque 

 rods and irregular bodies of iron oxide. This rock was found to contain 1 per 

 cent, of corundum. The nodules contain more corundum than the rest of the 

 rock, and enclose small round bodies like those observed elsewhere in the rock. 



(/) This rock also resembles sandstone in the hand-specimen. It is much 

 weathered, but consists mainly of deep-blue corundum in irregular grains. 



(g) (PI. XXX, fig. 5.) A sandy-looking rock, the base of which is greenish in 

 section and probably siliceous. In this are some dark bodies showing marked 

 concentric structure, and many round bodies of corundum which are replace- 

 ments of the former, and also exhibit in some cases concentric structure. 



(viii) 



Schists with corundum. 



Localities various. 



It has been found that corundum is present in some of the schists. 

 Unfortunately, none of the specimens are well preserved ; but tourmaline-corun- 

 dum rocks always occur associated with them. 



The sections frequently contain tourmaline. 



(ix) 

 Corundum-mica rocks. 



These are not common. Near Batu Gajah a large boulder was found lying 

 upon limestone. It had a rough and iron-stained surface, and was intensely 

 hard. A fresh fracture showed a dark greyish-blue rock, with veins of a bluish 

 material; and a magnifying glass showed that a platy mineral was present also. 



Q.J.G.S. No. 263. 2h 



