110 DISPOSITIONS^ FRACTURES &C. OF STRATA. 



sion of vertical veins. In Cornwall, where so many 

 veins are either vertical, or elevated at high angles, 

 this effect must have taken place in a very extensive 

 manner : but the most palpable instance on record is 

 that described as being found in Sky, in the account 

 of the Western Isles. At this place, the vertical veins 

 of trap are so numerous, as, in some places, to equal 

 in breadth one fourth of the including strata: through- 

 out the whole tract, they may be conjectured, without 

 any error that can affect this conclusion, to amount to 

 one twentieth. It is plain therefore, that the mass of 

 strata must have been laterally extended by so much ; 

 and it is evident that this cannot be explained by any 

 modification of subsidence, as the sides of the veins 

 are parallel. 



Till indeed some evidence is produced of the ex- 

 istence, or at least the probability, of such a cavernous 

 structure in the earth, we might, as we have been 

 desired to do, fairly withhold our assent from an hy- 

 pothesis which gives us no additional advantages; 

 which does not explain the appearances in an easier 

 manner, and which possesses the further defect of 

 being unconnected with any of the analogies or phe- 

 nomena by which the theory of subterraneous eleva- 

 tion is supported. Yet I trust hereafter to show 

 (Chap, xxi.) that there are appearances among the 

 strata that cannot be explained in any other manner; 

 and if the proofs then to be offered are admitted, it will 

 be established, not only that there actually exists, or 

 has existed, a cavernous structure of the earth, adapted 

 to the production of displacements by subsidence, but 

 that most important changes of that nature have been 

 produced in this very manner. 



