Table Lands of South India. 305 



The dykes are always divided into prismatic forms at right 

 angles to their length, and what is very remarkable, on the 

 sides these prisms are always displaced and canted slightly 

 upwards, so that the lower angle of the upper prism extends 

 beyond the upper angle of the lower one. Besides this, the 

 faces of the prisms on the sides of the dykes shew a vertically 

 channelled appearance, as if they have, when in a semi-pasty 

 state, been squeezed into a fissure ; and also the trap on the 

 sides of the dyke never adheres to the adjacent rock, as I 

 have remarked, it always does in dykes of basalt in granite. 

 I am not able to state whether the displacement and canting 

 of the prisms has place on both sides of the dyke, or only on 

 one, nor on which side I have generally observed it. Secti- 

 ons by which the side of a dyke is laid bare being generally 

 formed by the course of a nullah, it very seldom happens that 

 both sides are accessible at one place. 



In Salem and the Barramahal, the greatest portion of the 

 minerals found occur in the beds of this series : of these the 

 principal is Corundum. Magnetic iron ore also is found in 

 great profusion, both as a crystalline schist, composed of gra- 

 nular quartz, felspar, and magnetic iron ore, and in lumps or 

 crystals of two or three pounds weight. I am informed also, 

 that masses of two feet in diameter are found near Attoor in 

 Salem. 



Over the whole of the plain of the Barramahal and in Salem, 

 the surface of the granite is found at no greater depth than 

 20 or 30 feet. In the stony and gravelly plain of Trichino- 

 poly, granite is seen every where close to the surface, appear- 

 ing above it in numerous places. In the eastern part of the 

 table land of Mysore, I have shewn that the granite is to be 

 found close below surface. Dr. Benza, (Madras Journal, vol iv. 

 page 1,) informs us, that granite occurs at a short depth 

 below the surface of the plain of the Carnatic, and I believe 

 the same will be found to be the case as far north as 

 Berhampore. 



