GNEISS. ] 3 



patam. The Bezvada ridges and outlying bills are almost entirely 



composed of it, the only other strata being a few bands of quartz-schists 



and calcareous rocks, and thence to the north-east, in the Nifna 



Stalum country, it has a width of some 16 miles and so continues 



occasionally narrowing or widening out into the Golgonda country. 



Alongside of it, on the north, there is the less schistose, or even more 



massive band of gneisses, stretching from the Kondapilli hills, which 



answers more or less to those of the Nellore and Kistna areas. 1 



Indeed, so distinguishable is this form of gneiss in the area pointed 



out, that I gradually came to call it by the name here adopted ; 



and the area occupied by it is so great that it seems quite worthy of 



being considered as a fair group among tbe gneisses of the main or 



eastern area of the peninsula. I am as yet unable to draw a clear line 



of demarcation between it and the gneiss on its northern side, but the 



tentative boundary given in the map shows its general limits. The dip of 



the foliation, or, as it is to all appearance, lamination, is generally high 



and to the south-east, though folding and contortion are frequent ; and 



so far its later age over that of the Kondapilli gneiss, as evidenced by its 



less highly metamorphosed condition, is borne out. 



With the exception of the thin subordinate bands of quartz-schist and 



quartzose gneiss, the usual rock of this band 

 Lithology. 



is generally of a dark brownish-red colour composed 



mainly of a bright, lustrous, well- cleaved, and occasionally foliated red 



felspar. 3 It is rough and granular, but well foliated or more or less schistose 



1 See Parts 1 and 2 of this Volume of the Memoirs. 



2 Mallet writes — " Your mineral is murchisonite, a variety of orthoclase, the distin- 

 guishing character of which is the presence of an abnormal cleavage, making (in the 

 original mineral from Dawlish, in Devonshire) an angle of 106° 50' with the basal cleavage 

 and 90° with the clino-diagonal cleavage. These angles in your mineral are about 104° and 

 90°, or very near 90°. The lustre of Murchisonite on this abnormal cleavage is pearly, as in 

 your specimens. The latter in fusibility, &c., have the characters of orthoclase. The 

 hardness of the original murchisonite is rather less than that of felspar ; that of your 

 mineral is about 5 - 0. This low degree of hardness and the presence of free peroxide of iron 

 led me to think that the mineral was in an altered state, but its translucency when looked 

 at parallel to the pearly cleavage does not support this. It may have caught up the oxide 

 when originally formed." 



( 207 ) 



