of Salem and Barramahal. 171 



granite, as about the base of Royacottah hill. It seems pro- 

 bable, that the granite of Arran, which Dr. McCulloch men- 

 tions as being magnetic, may have owed this property to a 

 similar ingredient. 



Cleavage. 



In describing the red marie of Mysore, I have remarked 

 that the mamillar masses of granite split into concentric 

 lamina, upon heating the surface by a fire of wood. This is 

 maintained for several hours, and is then swept away, and 

 several large wedges are inserted under the edge of the 

 scale, which has separated. These are driven in by degrees, 

 until the plate has been bent up as far as its elasticity will 

 admit of. A workman then goes upon the surface with 

 a large hammer in his hand, and tapping upon it is able 

 to tell by the sound how far the fissure has run in ; at this 

 point he commences a series of heavy blows on the surface, 

 following up the fissure, as it runs on, assisted by the 

 wedges, until the plate gives way with a loud crash, rather 

 startling to any one who does not know what will happen, 

 and it is rent into several pieces, which are often scattered 

 about ; the man on the surface escaping by springing 

 nimbly aside. If the edge from which the plate is detached 

 presents a square corner, and a further fissure, a fire is 

 again made upon the surface, and a further scale detached, 

 which is generally thicker the further it is carried on. But 

 at last the broken part no longer presents a sharp corner 

 at bottom, but a rounded curve with the concavity upwards, 

 and the rock will then cleave no further, either by fire 

 or wedges. But if a fire is again made beyond the upper 

 corner, a thin scale may be detached from the surface, which 

 can be followed up as before. The lamina are not therefore 

 exactly concentric, but lie on the surface like the leaves of 

 an artichoke, with a sort of qua qua versal dip, and the 

 surface of the rock after a frequent repetition of the opera- 



