THE TRAP ISLANDS. 67 



The last remark refers to the interval of time which has 

 passed between the deposition of the secondary strata and 

 the period of that formation. That interval cannot indeed 

 be conjectured ; but undoubted marks of its existence, 

 though not of its length, are to be found in the same 

 phenomena. It has been shown, that the present dis- 

 jointed state of the strata is in many cases unconnected 

 with the influence of the trap, and that this rock has, 

 with certain exceptions, accommodated itself to those 

 portions which had been separated by the influence of 

 former causes. Of the nature of the causes which have 

 produced such evident marks of waste on the earth's 

 surface, it is unnecessary to inquire ; nor are they within 

 the limits of the proposed investigation. It is sufficient 

 for the present purpose, that changes so considerable 

 must have occupied time ; and that some interval, pro- 

 bably great, had elapsed between the period at which 

 they were effected and that at which the trap rocks were 

 superimposed on their scattered remains. 



It is now necessary to examine the relations of Mull 

 to the adjoining mainland, and to inquire respecting its 

 connexion with the northern islands of the group in which 

 it has here been placed. 



This island offers but few points of general comparison 

 with the preceding, and even less with that part of the 

 continent to which they are nearest. Moreover, the 

 difficulty which there exists in tracing the connexions 

 between the disjointed portions of the primary or se- 

 condary strata, encumbered and separated as they are 

 by mountains of trap and other unstratified rocks, exists 

 here in a much greater degree. 



The granite of Mull must be considered as an insulated 

 mass; but in this respect it is not peculiar, since that 

 rock occurs under similar circumstances in the neigh- 

 bouring districts of Strontian and Morven, as well as in 

 many parts of the adjoining continent. 



With respect to the primary strata which succeed it, 



