GNEISSIC ROCKS. 37 



nance of granitoid forms of crystalline rocks. As already mentioned 

 when describing the granular quartz rock outcrops in the neighbourhood 

 of Madura, they form from their bright colours and great bareness 

 very conspicuous features in the landscape, especially along the railway 

 from Kovilpatti down to Tinnevelly aud all round Palamcotta. The 

 greatest show is made in the rocky ridge south of Kovilpatti, which cul- 

 minates in the Kurumalai (Trigonometrical Station) a picturesque hill 



821 feet high, and in the Vallanad hills (see ante, 



Vallanad section. i-i n^/^^.o(>J/^nr'-» 



page 25) which attam a height or 1,023 teet (i,U52 



feet according to the Madras Revenue Survey map). The thickness of 

 the beds here exposed is very great, and maybe estimated at fully 2,000 

 feet, but the section is not clear enough to allow of actual measurement. 

 To the south of the Trigonometrical Station peak the dip, where 

 distinct enough to be measurable, is from 65^^ to 70° westward, and 

 the rock approaches in appearance to a glassy quartzite, from which 

 Texture and colour of i^ o^V differs in the coarscness of the grain, 

 the rock, which feature however is much less conspicuous 



here than in many other outcrops. The prevalent colour here of the 

 least weathered parts of the rock is a dull pale pinkish-brown, else- 

 where whitish-drab or very pale reddish-white are the commonest 

 colours. Pale salmon colour was noted in the summit bed of the Pasu 

 Malai near Madura and in the ridge north-north-west of Kotampatti 

 Travellers^ Bungalow 15 miles north of Melur and 34< miles from Madura. 

 Owing to the economically useless character of this rock it is hardly 



ever quarried to sufficient depth to show its real 

 Mineral character. 



texture and composition. In most outcrops the 



only mineral seen to occur in the minute spaces between the different 



quartz granules is an earthy (? decomposing) hsematite. It was nowhere 



so well seen as in the bed north of Kotampatti, just referred to. This is 



often absent having either been weathered out or having never existed in 



those spaces. In some examples the rock shows small cavities filled 



with white or pale pink decomposed felspar, and in one case I found 



traces of much decomposed greenish hornblende. This was in stone 



( 27 ) 



