238 INTRODUCTION TO THE TRAP ISLANDS. 



with their more sparing occurrence as we recede from 

 those central masses. I shall indeed hereafter show, that 

 their numbers can scarcely be reckoned in the immediate 

 vicinity of many of the masses of trap in Sky and in 

 Arran ; while they disappear in succession as we remove 

 from these, their progress being generally limited, although 

 in a few instances surprisingly persevering.* Hence we 

 may infer, that these veins are processes from the main 

 bodies of trap; and this view is occasionally confirmed 

 by the facility with which they can be traced to their 

 sources, examples of which are of frequent occurrence 

 in Sky and in the islands on the coast of Lorn. It is 

 not however pretended that this origin is universal, since 

 it is equally certain that two distinct sets of trap veins 

 exist; the posteriority of the one being proved by its 

 traversing the other, as well as by its distinctly intersecting 

 the great masses themselves. It is possible that many 

 of the more remote and persistent veins may be of the 

 secondary order, but of this we are not likely to obtain 

 any proofs. 



I shall now proceed with the details of the individuals, 

 commencing with Rasay, and treating of them successively 

 in that order which, however irregular it may appear, 

 seems most conducive to their mutual illustration. 



* The Argyllshire coast presents a striking illustration of this fact. 

 They are exceedingly rare between the Mull of Cantyre and Crinan ; 

 but beyond this they begin to prevail, and as we approach the great 

 mass which covers Mid Lorn, they occur in great abundance, increasing 

 in number and magnitude in proportion to their vicinity to that extensive 

 tract of the parent rock. 



