48 EOOTE : GEOLOGICAL STRUCTURE OF THE EASTERN COAST. 



The next outlier of the Kadapas requiring mention in these pages 

 occurs 85 miles to the north-east-by-north of the 



irava lpaya last-named one. It is one possessing considerable 



interest on account of its remarkable stratigraphical position, the pecu- 

 liarity of which consists in the mass being an elliptical anticlinal dome 

 let down among the gneissic beds by a series of faults, by which 

 it has been cut into an elongated rather irregular hexagonal area, 

 whose major axis extends about 7 miles north -east-by -north, the 

 minor measuring about 5 miles from north -west-by- west to south-east- 

 by-east. 



The top of the dome has been much denuded, and the quartzites 

 and other rocks cut away so much in the centre of the ellipse, that the 

 underlying granitoid gneiss has been exposed in a narrow longitudinal 

 valley, in which stands the hamlet of Biravallipaya. The dome is 

 made up of four principal quartzite beds, which are separated from each 

 other by three bands of slate. Here, as elsewhere, wherever the base- 

 ment of the Kadapa rocks is seen, it is formed by a quartzite. As 

 seen from the south-west, the slope of the hills is characterized by the 

 bare surface of one of the quartzite beds dipping south-west at an 

 ano'le of 30° ; and which presents very much the appearance of a glacis 

 leading up to the walls of a great fort. The dip of the beds on the 

 south-east and east side of the dome is from 45° to 50°, showing the 

 anticlinal to be an unsymmetrical curve. The highest remaining part 

 of the dome, which lies near the northern end, attains the elevation of 

 1,379 feet over sea-level, and is crowned by a trigonometrical station. 

 None of the beds exposed in this Biravallipaya dome could be identified 

 with the beds forming the eastern part of the Nakarikallu elliptical anti- 

 clinal, though they are separated by so small a distance. 



A similarly faulted dome forms the outlier west of Atchammapetta, 



and about 5 miles south- west-by- south of Chin- 

 Atchammapetta outliers. . . ... n 17 . , . T . . 



tapilly, on the Kistna river. In this case the 



out-lier has a rudely trapezoidal figure in plan, the greatest length 



of side being about 1| miles. It forms a low broad -backed hill, of 



( 48 ) 



