the Eastern Portion of the Basaltic District of India. 541 



another, although extensive plains intervene ; while, at no great distance, the 

 sandstone which forms the summits of these hills is seen on the same level 

 as the surrounding- plains. Numerous instances also occur in which the 

 original continuity of the horizontal summits is easily traced ; the strata on the 

 opposite and nearly perpendicular sides of a valley being similar, but having 

 a considerable dip, the beds descend to the general level of the country. A 

 good example of this is seen, in Section 2, Pl.XLVI._,atChintagooutaand Gun- 

 dicottah. These anomalies were at first quite inexplicable, nothing appearing 

 in the valleys but a rich alluvium, nor on the summits (which are reached with 

 much difficulty) but a sandstone perfectly horizontal, and divided into huge 

 tables by perpendicular partings, sometimes separated several feet from each 

 other, and filled with broken pieces of the rock. This jointed structure is 

 common to the sandstone, the schistose beds on which it for the most part 

 immediately reposes, and the stratified limestone into which these schists pass 

 insensibly ; but the size of the tables so formed, varies from rhombs of a few 

 inches, in the schist and lower part of the sandstone, to enormous masses on the 

 summits of the hills. Nowhere is this structure and the succession of strata, 

 of which it is characteristic, better seen than in the table land in which are si- 

 tuated the celebrated diamond mines of Bangnapilly and others now deserted. 

 The accompanying wood-cut will give some idea of one of these mines. 



Table Land of Bangnapilly. 



Diamond Sandstone 





Schistose Beds passiii; 

 into LimestoiK 



Diamond Mines 



The plains at the base of the table land of Bangnapilly consist of a rich black 

 alluvium, containing fragments of basalt, jasper, and the various minerals found 

 in the hills. It rests on a fine, compact, dark blue or nearly black limestone, 

 which contains much argillaceous and siliceous matter. This limestone 



4 A 2 



