62 HOLLAND: MICA DEPOSITS OF INDIA. 



of this younger envelope, and it is unknown, of course, how much 

 valuable material is so hidden by these deposits. 



A grey gneissoid granite, at times hornblendic, at other times 

 containing both micas so as to become a normal granite, and large, 

 ill- defined masses of hornblende-plagioclase rock intervene between 

 the schist complex and the Cuddapah rocks which form the 

 Veligondas. 



Near Gilakapad (i4°l5'; 79°4o') an interesting quarts-porphyry 

 was found. Two narrow aphanitic dykes of diabase run east and 

 west intersecting the quartz-porphyry. 



The diabase-dykes which are seen in frequent outcrops throughout 

 the district are most abundant towards the west in the vicinity of 

 R^piir. They are sometimes augite-plagioclase rocks and sometimes 

 olivine-diabases. - 



Laterite very often forms the surface rock along the east of the 

 schist complex, while to the north of the Penner river in the mica- 

 belt, kankar is very abundant, being as a rule of the same distribution 

 as the hornblendic rocks, from which it is very probably derived. A 

 few miles east of Kaligiri a long narrow ridge borders the Kaligiri- 

 KaVali road on the north side. This ridge is peculiar in that it is 

 composed of well-rounded quartzite boulders, while elsewhere the 

 loose rocks are almost always angular or sub-angular. As it is 

 generally supposed that at no very distant geological time the sea 

 extended inland to the Veligondas, it may be that this ridge owes its 

 origin to the action of the sea on a former quartzite outcrop whose 

 rocks were broken and rounded by the action of waves on the 

 beach. 



The pegmatite masses are generally in the form of intrusive sheets 

 or dykes following the foliation of the schists, very rarely cutting 

 across the folia. At times the dykes are of considerable thickness 

 though some of the very thick masses are lenses, and still others are 

 of indefinite form. They are most frequent in schists dipping at high 

 angles. No well-defined contact action has been observed, though 

 ( 52 ) 



