124 KERHEilA. GEOLOGY. 



The relation of the trap to the sandstone and conglo- 

 merate, is by no means so clear; yet as some decided 

 instances occur of its overlying position with respect 

 to these also, we are perhaps justified in concluding, 

 that the whole of the trap is posterior to the stratified 

 rocks whether primary or secondary ; and that wherever 

 it appears inferior to the latter, the apparent priority 

 implied by this, is only an example of intrusion similar 

 to that which occurs between the trap and the schists. 



The confusion naturally attending this rock, is much 

 increased by the great number of trap veins which are 

 independent of these ramifications and of the principal 

 masses ; and which are proved to be so by their passing 

 through the trap as well as the stratified rocks in an 

 uninterrupted course; having the ordinary characters of 

 the usual veins so frequent throughout Scotland, and so 

 prevalent in the vicinity of the great masses that con- 

 stitute Sky, Mull, and the associated islands. Their 

 posteriority to the masses of trap is in some cases 

 distinctly seen ; although in many, when they are 

 similar in character and composition to the rock they 

 traverse, it is difficult to distinguish them from those 

 which are only branches of the mass ; since, from wea- 

 thering in the same manner, their most ordinary and 

 obvious distinguishing characters are obscured. 



The variety of composition that occurs in the trap 

 veins, is considerable; and it is remarkable, that both 

 here and in the neighbouring islands where they also occur, 

 their characters are often unusual; partaking of those 

 of the larger masses in the neighbourhood, and consisting 

 of the several varieties of compact felspar or clinkstone * 

 which compose these, rather than of the greenstones and 

 basalts of which they are more generally formed in other 

 places. It is probable, that in as far as they are formed 



* I have not attempted, in the account of this island, to assign the 

 exact name to this rock, because it appears to be often of an interne- 

 diate character. 



