502 GENERAL COMPARISON OF 



mark is confirmed here ; not only by the position of the 

 trap in the islands under review, but by the place which 

 the analogous portions already noticed, occupy on the 

 mainland. This association is in some points indeed very 

 conspicuous in these islands. In Arran in particular, it 

 was shown that the Machrie river formed the mutual 

 boundary, as far as it extended, between the primary 

 and the secondary rocks ; inasmuch at least as the prin- 

 cipal mass of the latter was concerned. The same river 

 is also the boundary of the trap rocks ; none of which 

 are found to pass it; nor, except in the form of veins, 

 to intrude in the slightest degree on the primary strata. 

 A striking instance of the nicety of this arrangement, 

 occurs on the brow of a hill lying above the joint opening 

 of Glen Rossie and Glen Shira, and not far from the 

 source of the Machrie. A small mass of trap is here 

 found, far detached from the prevailing portions, and 

 lying on the very borders of the sandstone, just where 

 it is about to terminate finally in the schists of the moun- 

 tainous region ; on which it does not intrude. The same 

 remark may be made on Bute, where the trap is equally 

 limited to the secondary division of the island. 



On the mainland, a similar distribution will be found 

 to prevail. The ranges of Fife, of the Ochils, the Sidlaw, 

 the Pentland, the Campsie, with all the minor tracts of the 

 same rock, are to be found equally connected with the 

 secondary strata ; sometimes immediately imposed on the 

 red sandstone, in others on the later strata which lie 

 above it. The same association will be found on the 

 shores of Cantyre in the vicinity of Campbeltown. Con- 

 siderable masses of porphyry, of which the rock of Devar 

 is among the most conspicuous, occur in this tract ; and 

 in every instance they appear to be connected with the 

 red sandstone or with the coal strata above it. Even in 

 those cases where these masses are in contact at one part 

 with the primary rocks, their larger portions will be found 



