318 On the formation of the 



piece of rusty shell. When the softest of such blocks are 

 exposed to the air, the upper surface often breaks up, and 

 becomes disintegrated, exposing the spheroidal structure in a 

 series of diminishing rings or steps, shaped like a Roman 

 amphitheatre in miniature ; whence many persons have ima- 

 gined, that the action of the air has produced the peculiar 

 structure. This, however, is totally incorrect, and I have seen 

 blocks in which two centres of spheroidal structure are plain- 

 ly to be seen, and besides, the concentric lamina of both are 

 traversed by the same fissure cutting through the whole of 

 the block: which is a complete proof, that the structure is 

 original. I have a specimen of about nine inches in diameter, 

 being the centre of a block which was soft and friable, and in 

 which the concentric lamina of about \ inch in thickness are 

 divided from each other by a perfect thin film of white carbo- 

 nate of lime. 



On the road between Royacottah and Kellamungalum, 

 about three miles east of Anchitty, may be seen a mass of 

 greenstone rock, which in parts is friable, and several yards 

 wide. It shews the concentric lamillar structure perfectly 

 plain, with several centres ; the concentric rings being marked 

 by dark rings, which coincide with the scales into which the 

 rocks divide. The concentric divisions are not circular, but 

 bent into irregular curves, which do not interfere with each 

 other. In two places, irregular-shaped smooth masses of 

 black granite are embedded, the upper half being denuded 

 and exposed ; around these, the concentric lamination of the 

 greenstone coincides with the irregularities of the surface, and 

 in one part where the central mass is split into two pieces, 

 and the part slightly separated, the lamination of the green- 

 stone bends in a curve into the hollow of the fissure. Near 

 the mass of black granite, the lamination is very thin and 

 fine ; but is rendered perfectly apparent by the same thin 

 leaves of carbonate of lime alternating with it. In the large 

 mass of greenstone layers of carbonate of lime, ith inch in 



