GENERAL COMPARISON, &C. 59 



GENERAL COMPARISON OF THE TRAP ISLANDS.* 



IT will now be convenient, for the purpose of general 

 scientific views, to bring into one collective statement the 

 leading particulars in the structure of the islands of this 

 group, as far as they possess any relations to each other. 

 Thus, those local details, of which the interest would 

 otherwise be limited to a narrow space, become of im- 

 portance by their mutual dependence ; and such a con- 

 tinuity of structure is thus by inference restored, as would 

 follow, either by replacing the portions that seem to have 

 disappeared from among these islands, or by removing 

 the obstacles which cause the present semblance of dis- 

 continuity where, in a geological sense, it may not actually 

 exist. In attempting thus to bring the whole under one 

 general view, it will be necessary to recapitulate many 

 particulars ; but the unavoidable repetition occasionally 

 arising from this, will be compensated to the reader by the 

 greater facility that will thus be afforded to him in under- 

 standing their connexions, than if he had been suffered to 

 draw the comparisons for himself. 



Notwithstanding the set of common characters by which 

 the whole group of the Trap isles is united, there is one 

 common feature existing in Sky and the neighbouring 

 islands, in which Mull can scarcely be said to participate ; 

 while that portion of the group is also associated by a 

 certain intimacy of geographical position, from which this 

 island is in a great degree excluded. The connexions of 

 the former subdivision with the continent, are also formed 

 by the primary strata solely ; while those of Mull with the 

 adjoining land, are to be traced chiefly in the secondary, 

 and in the masses of trap which cover them. A corre- 



* See the general Map. 



