Relations of the Secondarij Strata in the Isle of Arran. 35 



the upheaving forces must have been in action some time after the deposition 

 and consolidation of the new red sandstone. It also follows that the granite 

 could not have been in a fluid state at the time of its elevation ; for had that 

 been the case^ it could never have risen into lofty mountains and mural pre- 

 cipices, overhanging the secondary strata, without ever flowing over their 

 broken edges, or penetrating their mass in the form of dykes. The phseno- 

 mena at Tornigneon, before alluded to, may seem opposed to this conclusion. 

 But we must remember that at the time of the elevation of the granitic nucleus, 

 all parts of it were not necessarily at the same temperature. It is also pro- 

 bable that the first dislocations of the primary slate were not contemporaneous 

 with the last elevation of the granite, by which the secondary rocks were 

 broken in the manner above described, and upheaved into the positions they 

 now occupy. 



VI. If it appear from the preceding statements that the granite, in its pre- 

 sent form, is posterior to the new red sandstone, we may also remark, that the 

 trap of the southern division of the island is also posterior to that formation. 

 For the trap not only traverses the sandstone in places without number, but 

 has flowed over it, and formed mountain masses of overlying rock. It must, 

 therefore, have been in a much more fluid state than the granite at the time 

 of its eruption : and this is probably the chief reason why the stratified rocks 

 are so incomparably less dislocated in the southern region of the island than 

 they are in the northern. 



VII. Respecting the exact age of the trap, we have no secure grounds of 

 conjecture : in this respect, the only thing we can certainly determine is the 

 limit of its antiquity. There may have been several periods of eruption : for 

 the greatest part of the trap of the Hebrides is newer than the oolitic series, 

 and in the north of Ireland it is newer than the chalk. 



The data for determining the epoch of the last elevation of the granite of 

 Arran are perhaps still more imperfect. As, however, all the elevated forma- 

 tions in the northern division of the island are occasionally traversed by trap 

 dykes, we have a proof that those internal movements which produced the 

 great eruptions of trap must have had their origin below the foundations of 

 the granitic mountains. If these eruptive forces were not able to break through 

 the thick covering of granite and primary schist, they may have acted on them 

 in the mass, have partially penetrated them, and been the very agents by which 

 they were lifted up to their present elevation*. 



* The hypothesis advanced in the text is in accordance with what we observed in many of the 

 primitive districts of Scotland. On reaching the centre of elevation we did not always find granite, 

 but often found gneiss penetrated by granite veins. The analogy, presented by actual junctions 



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