412 ARRAN. GEOLOGY. OVERLYING ROCKS. 



one is to be observed running parallel to a vein of 

 felspar rock formerly described, resembling it exactly 

 both in position and dimensions. They are also found, 

 together with veins of porphyry and of pitchstone, near 

 Tormore; where they are however no otherwise con- 

 spicuous than as they are posterior to the latter, and 

 add to the general confusion of this intricate spot. 

 They also occur in the course of the Sliddery water; 

 but are perhaps most conspicuous between Coryravie 

 and the Bennan head, where they run like walls far 

 out into the sea ; sometimes forming commodious break- 

 waters for small boats, and offering excellent foundations 

 for piers, were such buildings wanted. 



I formerly observed that trap veins are also found 

 traversing the granite, but they are much less frequent 

 in this rock than in the secondary strata. The cause 

 of this will not appear difficult of explanation, when 

 the circumstances formerly pointed out in the trap veins 

 of Strathaird are recollected. It was there shown, that 

 the greater number of these might be traced with much 

 probability to the overlying masses of trap in the 

 immediate vicinity, and that their courses were limited ; 

 often indeed confined to a very narrow range. The 

 same consideration will explain their greater frequency 

 in this island among the secondary strata ; since the 

 overlying masses are invariably superincumbent on these, 

 and remote from the granite, which has thus been 

 penetrated by only a few of the most persistent ; possibly 

 indeed, by veins of an independent nature, and of an 

 era different from that of the overlying masses. 



These veins occur in Glen Rossie, but without any 

 peculiarities requiring detail. A very conspicuous one 

 is also to be observed at the head of Glen Sannox ; 

 and of these I may remark in general, that their contact 

 with the granite is always perfectly denned, and that 

 neither substance appears to undergo the least change 

 at the place of junction. Occasionally every other rock 



