356 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



designated by the name of diamond-sandstone. Now, although the 

 diamond-conglomerate has been found reposing on sandstone beds, 

 yet there is no instance, that I am aware of, of the diamond having 

 been extracted from any one of them; nor are there any data to 

 prove that the conglomerate derived most of its materials from that 

 source. On the contrary, Heyne * has shown that the pebbles at 

 Kondapetta and Ovalampalli, near Kaddapa, are chiefly of chert and 

 jasper-basalt, quartz, hornblende, and felspar. The first two have 

 evidently been derived from the limestone of the neighbourhood, and 

 the rest from igneous rocks. And these pebbles are not contained 

 in a paste of sand, but, according to Heyne, of clay f . It is true 

 the diamond- conglomerate may in one place overlie sandstone ; but 

 in another place, as at Kondapetta, it may rest upon limestone, 

 while in a third, as at Bejwa<:/a, near Masulipatam, according to the 

 statement of Captain Newbold, it may be found immediately above 

 gneiss ;jl. In short, I am inclined to concur in the verdict long ago 

 pronounced by that experienced Indian observer. Dr. Heyne, when 

 he remarked, "All the diamond-mines which I have seen can be 

 considered as nothing else than alluvial soil" (superficial deposit). 

 But if the matrix of the diamond be a surface-deposit overlying 

 several rocks, I can perceive no propriety in attaching its name to one 

 of these more than another. The matrix at Weiragac? is a lateritic 

 grit, and it is worthy of notice, that wherever the precious gem is 

 sought for, whether in India or Brazil, there for the most part oxide 

 of iron is diffused. 



Having myself met with no fossil in this formation, I have nothing 

 to offer by way of determining, its precise age, but would content 

 myself with remarking, that it must be posterior to the overlying 

 trap, on which it is found occasionally, though in our district very 

 rarely, to rest. 



IV. V. and VI. Trap and its enclosed sedimentary Formation. — 

 The next rock to Laterite in order of downward succession is the 

 overlying trap, with which, however, for the sake of perspicuity it 

 will be necessary to combine the freshwater formation previously 

 alluded to and the underlying trap. 



Trap, it was before stated, is the prevailing formation in the west 

 of our area ; but when that assertion was made, it was understood 

 that this volcanic rock is of two kinds, — one overlying, and the 

 other underlying, — and that between these two, and therefore seldom 

 exposed to view, there is for the most part found an aqueous de- 

 posit. All three generally occur together. The exceptions are met 

 with in the plains, on the outskirts of the trap-formation, where we 

 not unfrequently observe the usually enclosed stratum resting im- 

 mediately on sandstone without the presence of either the upper 

 or lower basalt. In some of these instances it is probable that 

 the overlying rock has been removed, and cases occur of its re- 

 maining where no underlying trap has ever existed. On the other 

 hand, there are examples in similar border-lccalities of a single sheet 



* Tracts on India, p. 97. t Ihil. pp. 96 and 105. 



X R. As. Soc. Jour. vol. viii. p. 245. 



