42 FOOTE :' GEOLOGICAL STRUCTURE OF THE EASTERN COAST. 



3. — Intrusive rocks in the Gneissic area. 

 All the intrusive rocks occurring- within the gneissic area being, as far 

 as at present known, of greater age than the overlying Kadapa rocks 

 which they are nowhere seen to penetrate, it will be convenient to con- 

 sider them before proceeding further. The intrusive rocks seen are 

 referable to the following four groups : (a) Trap dykes and intrusions ; 

 (I) Granite veins ; (c) Felsite veins ; (d) Quartz veins. 



a. — Trap dykes and intrusions. 



As compared with many other parts of the great gneissic region 



„ .. . . of Southern India, the Guntur-Ongole area is 



Rarity of trappean ' ° 



rocks. remarkable for the extremely small number of 



trappean intrusions that have taken place in it. Not only is the number 

 of such intrusions small, but they are mostly of very small size, and in 

 eveiy way of extremely small importance geologically. One exception 

 may perhaps be made, but in this case the really trappean character of 

 the rock is very doubtful ; it relates to the black hornblendic mass of the 

 Enemerla hill east of Pamur, already described above (see page 38). 

 From its isolated position this mass suggests the idea that it is intruded 

 among the highly schistose beds which surround it ; but unfortunately 

 the contact between the two could not be traced. The petrological 

 characters of the mass are so extremely like some of the other highly 

 hornblendic metamorphic beds, that they do not afford, without special 

 chemical or microscopical analysis, sufficient evidence safely to decide 

 their exact nature. The same remarks apply, though in lesser degree, to 

 the equally doubtful hornblendic rocks of the Ianakotai hill occurring 

 6 miles to the east-by-north, near the village of Ayawarpalle. 



All the other unquestionably trappean intrusions occur in the form 



of true dykes. The greatest number of these 

 Dykes. . 



occur in the granitoid gneiss region around the 

 Bellam Konda, in the Kistna valley. A few occur in the lower part of 

 the Gundlakamma valley, and a small group in the upper valley of the 

 ( 42 ) 



