Reviews — Bryce's Geology of Ayr an. 553 



not been "witliout acknowledgment ; it is of more importance, there- 

 fore, with all respect to the author, to point out any faults or defects 

 that may still appear in it. 



The general succession of rocks in Arran has long been pretty 

 well made out, having been investigated by many able geologists, 

 from the days of Jamieson and McCulloch, down to those of 

 Sedgwick, Murchison, Ramsay, and Lyell. A "central nucleus" 

 of granite, forming the lofty jagged ridge which so arrests the eye 

 from various points of the Firth of Clyde, and which is found to 

 have burst through and uptilted the older stratified rocks in its 

 neighbourhood, consisting of successive bands, more or less entire, 

 of Clay-slate, Old Eed Sandstone, and Carboniferous deposits, — so 

 far all is comparatively plain sailing.^ The two " straits" or difficult 

 passages in Arran geology may be said to be (1) "the two granites," 

 and (2) the " glacial phenomena," — the one in some respects peculiar 

 to Arran, the other more general, or pertaining also to other 

 localities. 



The granite which forms the mountainous district of Arran is 

 found to consist of two kinds, — coarse-grained and fine. Some ob- 

 servers hold that these are mere local varieties of one and the same 

 rock, just as there are similar varieties in other rocks, whether 

 ordinary-stratified, metamorphic, or eruptive ; and that, for anything 

 that appears, both are of the same age, having been upheaved sub- 

 sequently (Jioio long subsequently we know not) to the deposition of 

 the Carboniferous strata. But Dr. Bryce, apparently not satisfied 

 with this, proceeds to discuss at considerable length (pp. 21-28) 

 " the relative ageof the granites." Let us see, then, what he makes of it. 



Apart from the " nucleus," there are in the island two outlying 

 tracts of granite, both of the fine variety, one of which has been 

 erupted amidst Carboniferous strata, and is therefore " clearly of 

 later origin." The other, at no great distance, occurs either in the 

 Old Eed, or at the junction of this rock with the Carboniferous strata, 

 rendering its identity of age with the first-mentioned " extremely 

 probable." The granite of the nucleus, however, does not actually 

 come into contact with either the Old Red or Carboniferous rocks ; 

 but at those points where it comes nearest to them (v/ith a narrow 

 belt of slate intervening), we find these formations uptilted steeply 

 towards it, the Old Red being in some places considerably altered, 

 and the Carboniferous strata overlying it, in general, conformably, 

 or at a corresponding angle of disturbance or elevation. These cir- 

 cumstances, taken along with the fact that there are no luorn frag- 

 ments of the granite found imbedded in the sandstones of either 

 formation, seem to yield every proof that the nature of the case 

 admits of, that the upheaval of the granite, whether coarse or fine, 

 was at least post-Carboniferous. 



^ Yet even liere a curious mistake has lately been made. In the short article on 

 Arran in Chambers's excellent OyclopcecUa, we find it stated that " Lias and Oolite lie 

 on the Mica-slate." Well may the student of Arran geology exclaim — 

 " Far ha'e I travelled and meikle ha'e I seen, 

 But Lias on the Arran slates never saw I nane !" 



