198 GENERAL REMARKS [Ch. X- 



larly rounded masses, as in various parts of the British Isles, 

 being insulated, at the surface, in the slate, and intimately 

 connected therewith. These masses fluctuate greatly in their 

 dimensions; even those of the Ocrynian range vary from 

 fifteen miles to a few hundred feet in diameter : then again, 

 from this size to a small nodule, every intermediate link is 

 afforded by another series of granitic masses, which are 

 known to be perfectly insulated in the schistose rocks ; and 

 which, we have just seen, have the same relations to the con- 

 taining slates, as the large masses which have hitherto been 

 detected in .an insulated state only at the surface. Reason- 

 ing by analogy, it might be supposed, that all these masses of 

 granite, whether large or small, possess the same constitution : 

 the difference of dimensions being the only point, in which 

 it can be positively asserted that they are not identical. As 

 regards the layers or beds of granitic rocks, in the primary 

 slates, experience has taught us that they possess the same 

 characters ; differing from each other only in the degree of 

 their extent, but not in the nature of their associations with 

 the schistose rocks : indeed, they can scarcely be considered 

 in any other point of view ; since, by the gradual passing of 

 rounded into elongated masses, it appears to be demonstrated, 

 that these forms are convertible into each other ; and, there- 

 fore, are not indicative of different natures, being only modi- 

 fications of the concretionary structure resulting from the 

 various modes in which the integrant particles of the mass 

 are arranged. 



We cannot, indeed, draw any line of demarcation between 

 the smaller and larger masses of granite, whether contained 

 in the slate as rounded groups and patches, or interstratified 

 therewith as elongated layers or beds : and since the beds of 

 granite, alternating with slate near the junction of the main 

 mass of the former rock, are proved to be of the same nature 

 as the main mass, by their sometimes forming an integrant 

 part of the layers of which the latter is composed, what dis- 

 crimination can be made between such granitic beds and 



