%66 L1SMORE. GEOLOGY. 



the clay slate, which is here interlaminated with the strata, 

 occasionally predominates for a small space so as nearly 

 to exclude the limestone. It is perhaps unnecessary to 

 add that it is a primary rock. 



Natural caverns occur among these beds in different 

 places; of no great extent, but generally containing large 

 and ancient stalactitic concretions, the further increase of 

 which seems long since to have ceased. In the interior, 

 they much resemble the similar concretions of Gibraltar 

 and of Sicily, which have been so often wrought for 

 purposes of ornament. 



The rocks are much traversed by veins of calcareous 

 spar, of quartz, and of these two substances united. These 

 veins are commonly small, frequently veiy minute, and 

 a certain class of them follow the contortions of the 

 rock in which they lie. The whole question relating 

 to contortions is so obscure, that it does not mate- 

 rially add to the difficulty to imagine that the veins of 

 quartz had undergone this process conjointly with the 

 rock in which they are situated ; although we have at 

 present no conception of the mode in which quartz could 

 be softened so as to undergo this change. The pheno- 

 menon is however by no means uncommon, since it occurs 

 also in the parallel granite veins that traverse gneiss. 



It is evident that in these cases, the quartz, whether in 

 the shape of a vein or a lamina, must have been formed 

 by deposition, or by secession of the containing parts and 

 subsequent infiltration, while the rock was in its straight 

 or natural form ; since the intricate examples in question 

 could not have been produced by either process in their 

 present state. It necessarily follows that the contained 

 vein was bent when the including rock underwent the 

 change ; and indeed the mutual relation which these bear 

 to each other is sufficient to prove that the same cause 

 operated simultaneously on both. That we cannot ex- 

 plain the process is no argument against the supposition ; 

 since it is but one of numerous instances where we must 



