540 ISLE OF MAN. GEOLOGY. SCHIST. 



connexion with the rocks that precede and follow it. As 

 already remarked in the account of Bute, if any such 

 series can be ascertained, which is distinct in geological 

 characters, both from the primary and secondary rocks, it 

 would be advantageous to confer on it a specific designa- 

 tion ; but even then it would be necessary so to distinguish 

 it by an appropriate term, as to prevent any confusion from 

 applying that of graywacke in a double sense. 



It is evident that the presence of organic remains does 

 not distinguish between clay slate and graywacke, as they 

 are found in those deposits which contain both these rocks. 

 Neither does this form a constant geological distinction, 

 even in the graywacke, as they are frequently absent in 

 those districts which have been assigned to the class of 

 transition rocks. It appears difficult, indeed, to discover 

 what are the characteristics of a class which is to be 

 denned by circumstances that are only occasional, which 

 occupies the same positions and maintains the same rela- 

 tions to the associated rocks as the primary, and which 

 does not form an intermediate member between the 

 primary and secondary strata, since it is often altogether 

 absent. 



This is not however the place to discuss so important a 

 geological question. It is sufficient to have thrown out 

 these hints to geologists of more experience, to whose 

 consideration they must now be left, while I proceed to 

 describe the structure of the island under review. 



Assuming now, that which will shortly be proved, namely, 

 that the schist of the Isle of Man constitutes a single mass, 

 its character as a primary rock is determined by its position 

 with respect to the granite, since it immediately follows 

 that rock. This is therefore another instance, in addition 

 to those already known in our own country, of the imme- 

 diate succession of argillaceous schist to granite, a fact 

 too common to require any remarks on the inconstant 

 order in which the primary strata succeed that funda- 

 mental substance. 



The next question respecting the schist is, whether its 



