410 ARRAN. GEOLOGY. OVERLYING ROCKS. 



to an earlier or later stratified rock, proves nothing. 

 Rocks intruding from below in a state of fluidity or 

 softness, whether that fluidity arose from an igneous fusion 

 or not, admit of no such registry of their ages. It is even 

 possible, that in the course of future investigation into 

 a set of substances hitherto imperfectly understood, the 

 felspar rocks may be found in some instances demon- 

 strably later, and in others earlier, than the rocks of the 

 trap division. 



A great resemblance is often found to exist between 

 some individuals of the felspar division and others of the 

 granite tribe, as well as between the latter and some of 

 the trap division. That resemblance holds very strongly 

 in comparing the transitions between the two divisions 

 of felspar rock and trap, with the gradations which occur 

 in the different kinds of granite. There are no greater 

 differences among the transitions of the two former than 

 can be observed in the latter ; specimens of which are 

 to be found, consisting at one extremity chiefly of felspar, 

 with sometimes mica, at others quartz, or else with both 

 these minerals superadded ; while, at the other, they become 

 so filled with hornblende that they can scarcely be dis- 

 tinguished from the greenstones of the trap family. It is 

 equally easy to trace the continuity between those two 

 extremities, in granite as in the overlying rocks ; the 

 varieties of aspect which it presents, being even greater 

 than those which occur among all the individuals of the 

 two divisions above described. In other respects there is a 

 considerable resemblance between granite and the rocks 

 in question; although these latter differ materially, in 

 forming beds which lie over the secondary strata ; whereas 

 granite has not yet been ascertained to lie over the pri- 

 mary in the same manner. 



Trap veins are abundant throughout the island, and, 

 as is invariably the case, they traverse all the rocks which 

 lie in their way. 



It would be a tiresome, and now a fruitless, task to 



