GRANITOID AREAS. 41 



The members of the gneissic series are generally too coarse in texture 

 Slaty cleavage in to snow tme slat J cleavage well; moreover, it 

 gneiss rocks. generally coincides with the edges of the planes 



of deposition, and is therefore easily overlooked. For these reasons but 

 very few instances of it were noted, the chief of these being among 

 the mica schists 7 miles to the north of Pamur, and the slaty schists 

 on the back of the Chendalur anticlinal (see page 29) ; but neither of 



Singular result of cleav- these are of an 7 s P ecial Merest. A case of some 

 age in quartzite. interest, of cleavage in a quartzite bed, was observed 



in the western arm of the synclinal curve formed by the beds which make 

 up the Picherla Konda (see page 14). In this case one of the lowest of 

 these beds (a little to the south of the village of Balla Venkatapur), 

 which has an east-to-west strike with northerly dip, is at the point 

 where it curves eastward an ordinary quartzite, showing no special 

 features; but as it extends westward it becomes cut up by vertical 

 cleavage planes \ which become more and more numerous westward, 

 and are lined with a film of greyish mica ; the quantity of mica 

 increasing with the number of cleavage planes, till, just as the spur 

 sinks down under the local alluvium of the adjoining nulla, the rock 

 is almost an absolute mica schist. The intermediate gradations were 

 instructive, showing the progressive changes dependent on a very pecu- 

 liar form of metamorphism. The half-way gradation had a strong 

 general resemblance to a coarse " blotchy " porphyritic gneiss, which 

 no one who had not seen the gradual change would be inclined to 

 regard as the possible outcome of extra-metamorphic action on a true 

 quartzite. 



A great show of cleavage of clayey mica schists may be seen in the 

 Nandana Marrila hills north of Kanigiri. In this case the cleavage 

 coincides actually, or very nearly, with the lamination of the true 

 bedding. 



1 They might be mistaken for jointing where they first begin to show, but a little 

 further west they become far too numerous to be regarded as anything but cleavage planes. 



( 41 ) 



