332 ON THE METAMORPHOSIS OF STRATA. [Ch. XIV. 



are so various at different points, that, as already stated in a 

 former chapter, sometimes the strata are concluded to have 

 been broken, sometimes both the strata and the gr anite 

 whilst in other cases the granite itself is shattered into frag- 

 ments, the strata remaining uninjured ; and, lastly, in some 

 places the granite has produced crystalline slates, penetrated 

 by granite-veins, indicative of interior ignition. These various 

 appearances, however, are not so contiguous but that they 

 might be imputed to numerous and distinct eruptions of 

 granite : but even admitting this to hold good in Caithness 

 and Sutherland, the same indulgence cannot be extended to 

 the Isle of Arran, where the red sandstone reclines near the 

 granite, in one place in an unaltered state, whilst, imme- 

 diately adjacent, primary slates abound, containing granite- 

 veins. And even if this objection should be met by sup- 

 posing the same mass of granite to have experienced suc- 

 cessive protrusions under different conditions, still it must be 

 remembered, that these are only ingenious conjectures, sug- 

 gested by the perplexing necessity of the case, and unsup- 

 ported by any known effects of the internal igneous power 

 now in operation. 



In conclusion, we contend that the analogy between the 

 primary and trap rocks is not perfect, the strata next the 

 former exhibiting a chemical as well as a mechanical dif- 

 ference ; and admitting the sedimentary strata to have been 

 changed by the contact of trap in a state of ignition, a most 

 perplexing difficulty arises, in the fact that the alterations are 

 only partial : what could possibly have been the peculiar 

 controlling circumstances which prevented a like cause from 

 producing the same effects ? 



