Mineralogy of Southern India. 209 



earthy. Ure defines it as soft and easily broken, in which 

 he differs from Macculloch. Might be called " Ferruginous 

 clay-stone," as all the specimens are highly ferruginous, and 

 coloured red from peroxide of iron : and then the connection 

 with rubble or red chalk, and red ochre, would be esta- 

 blished. 



Silicious Schist. 

 Not common : found only among rocks of the porphyritic 

 series on the Topoor ghaut. Fracture, even : small grains 

 of quartz visible in it. Is infusible. Colour, bluish black. 

 Is Lydian stone, according to Thomson's and Ure's defini- 

 tion ; but differs from flinty slate, in not having a slaty frac- 

 ture. According to Brooke's, is flinty slate ; is called black 

 jasper by some writers. Macculloch separates two kinds, 

 apparently much the same, into flinty slate, and a quartzose 

 variety of argillaceous schist, which he argues have a different 

 geological position. It seems to be a silicious variety of 

 basalt, as some varieties of basalt do not melt easily before 

 the blow-pipe, and only imperfectly intumesce a little, and 

 turn white, in consequence perhaps of being silicous. 



Felspar Porphyry. 



Is formed of large crystals of felspar, embedded in a crys- 

 talline base of resplendent felspar. The embedded crystals 

 are often of very large size, and sometimes of a beautiful 

 flesh colour, which gives the rock a very handsome appear- 

 ance. The felspar is characterised by being infusible, or very 

 nearly so, before the blow-pipe, and even in a smith's forge it 

 is hardly melted ; in which it differs materially from the fel- 

 spar of European petrologists. In character it does not seem 

 to agree with the felspar porphyry, described by Bakewell ; 

 because he describes the paste or base as being formed of 

 compact felspar (compact earthy felspar.) It graduates into 

 pegmatite and graphic granite. It is a common rock in the 

 porphyritic or schistose series, in which it forms extensive 



