Ch. II.] ASSOCIATION IN ALTERNATING BEDS. 21 



taining a parallel course. The nature of granitic countries 

 will not admit of this arrangement being traced to any great 

 extent ; which, indeed, is likewise the case with the schistose 

 rocks; for even their continuation is more frequently pre- 

 sumed than actually ascertained. 



Even, however, when the characters of these rocks are well 

 preserved over a given tract (that is, when they are distinctly 

 granite, protogine, or felsparite, as above defined), yet a nar- 

 row inspection of any individual bed or layer will exhibit 

 other kinds, in the form of veins, or insulated masses of 

 various forms and dimensions. 



The occurrence of a different granitic rock within another, 

 arranged in patches or clusters around, as it were, certain 

 centres of attraction, is of such common occurrence that it 

 seldom arrests the attention ; even when it does not consist 

 of precisely the same ingredients as the main mass, differ- 

 ently combined as to proportions, or to the size of the com- 

 ponent particles. But when these insulated compounds 

 assume an elongated form, of greater or less regularity, then, 

 under the name of veins, they have been considered more 

 interesting, and have given occasion to much speculation 

 concerning their origin. 



These granite-veins within granite, as they have been called, 

 are very numerous in the Land's End district ; and are beau- 

 tifully displayed in some parts of the cliffs near the Logan 

 Rock and Lamorna Cove, more especially on the shore, 

 where the rock is polished by the action of the waves. 



Mr. Carne has enumerated, in the " Cornish Transactions," 

 some instances of these veins in this locality, stating that 

 they are of three kinds : first, those which are of the 

 same composition as the containing rock, but rather 

 decomposed, and do not possess regular walls; secondly, 

 those which only differ in containing large red-coloured 

 crystals of felspar ; and, thirdly, those veins which are com- 

 pact and fine-grained, very different from the contiguous 



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