Ch. XIV.] OF THE STRATIFIED ROCKS. 503 



" The induration," says Dr. Berger, " which the secondary 

 rocks undergo, when traversed by dykes of trap, has often 

 been noticed ; it is not my intention now to discuss this sub- 

 ject: I shall only mention that the induration does not extend 

 far from the dyke, and that the phenomena, though very fre- 

 quent, are not universal." * " In general, there is no foreign 

 matter between the substance of the dyke and the rock it 

 divides, except a slight rusty appearance on the surface of the 

 latter. The contact between the two is pretty close, but they 

 may always be disjointed by the blow of a hammer." f 



Before proceeding to make any remarks on these observa- 

 tions, it will be well to relate the nature of the phenomena 

 alluded to, as detailed in the same paper, on the north-east of 

 Ireland, by the Rev. W. Conybeare. " At Redbay Castle, 

 several basaltic dikes traverse the conglomerate : one of these, 

 remarkable for its great thickness, having resisted the action 

 of the waves, which have encroached considerably on the 

 adjacent cliffs, presents some bold detached crags projecting 

 from the beach. The conglomerate forming the wall of the 

 dike has undergone a great degree of induration, its cement 

 assuming the appearance of a compact hornstone ; thus it has 

 been enabled to oppose to the sea a resistance almost equal to 

 the basalt itself, and is still seen adhering on the sides of the 

 advanced crags." J 



" The whin dike of Carrick Mawr forms a broad causeway, 

 traversing the beach, and terminating in a nearly insulated 

 mass of rocks rising about thirty feet ; of this mass only the 

 central line consists of the dike itself, the sides being evidently 

 composed of portions of the strata traversed by it, but much 

 altered in their character and degree of induration by its 

 contact. These beds appear to have been chiefly derived 

 from the slate-clay of the coal measures, which has become so 

 compact as to assume the character of flinty slate. In one 

 point, this rock may be seen on one side, and on the other, 



* Geol. Trans., vol. iii. p. 230. f Idem, p. 231. 



I Idem, p. 201. 



