8 foote: geological structure op the eastern coast. 



while in the northern it is entirely wanting-, and the prevalent strike of 



the rocks is more nearly vertical to the present coast line than parallel 



to it. Petrologically there are many important differences between the 



_._ „ ,, g-neissic rocks of our present area and those of the 



Differences from south- & r 



era gneissic rocks. gneissic districts above alluded to. The f acies of 



the northern gneissics is newer than that of the southern rocks ; they 

 have, on the whole, been less metamorphosed, but more disturbed by 

 flexures, or else the way in which the disturbing forces affected them has- 

 left more distinct traces. 



The most striking petrological difference, and that which especially 

 XT „ . „ gives rise to the newer-looking facies of the 



Newer facies ot => ° 



northern gneiss. northern gneissics, is the presence of numerous 

 important beds of quartzite interstratified with the older-looking highly 

 crystalline varieties. These quartzites are so singularly like the typical 

 beds of Kadapa quartzites, occurring in the overlying Kadapa system 

 in the Vellakondas and as outliers capping gneiss hills, such as the 

 Bairawudi Konda and (outside the limits)- the Udayaghiri and Korisi 

 Konda, that they immediately suggested the idea of their being really 

 members of the newer series, let down into their present positions 

 by a series of remarkable parallel longitudinal faults. It was only 

 after long- continued exploration of their relations that the conviction 

 forced itself upon me that they were truly members of the gneissic 

 system. My reasons for arriving at this conclusion will be stated 

 further on. ^- 



Another point of difference is the greater development, in proportion 

 to the general area, of highly micaceous and chloritic schists in the north- 

 ern area, which for convenience I will call the Kistna-Nellore area. 



A third point of difference may be observed in the large develop- 

 ment of syenite -gneiss, of much more intensely hornblendic form than 

 is common anywhere in the more southern parts alluded to. 



Fourthly, may be mentioned the occurrence of considerable beds of 

 mica schist highly charged with staurolite and kyanite crystals, a rock 

 ( 8 ) 



