1852.] NICOL ON THE GEOLOGY OF CANTYRE. 423 



strata in the south of Scotland ; and expressed my belief that these 

 two formations were the two sides of a great synclinal trough in 

 which the coal-formation was deposited. The facts above-noticed 

 seem to add confirmation to this view. In mineral character the 

 beds are intermediate between the Silurian slates and greywackes 

 in the south, and the crystalline strata on the north. The position 

 of the beds corresponds to this view. The peninsula of Cantyre 

 is as it were the outcrop of the western extremity of the long 

 trough-like basin of central Scotland. I have not examined the 

 upper part of the peninsula between Skipness and Loch Tarbert, but 

 have little doubt, from its physical geography, that the strata there 

 will be found curving gradually round into the normal E.N.E. di- 

 rection of the central Highlands. The clay-slate in Arran shows the 

 same curve, but thrown off much further to the east by the intrusion 

 of the granite of Goatfell, which, however, took place at a more 

 recent period, or after the deposition of the carboniferous strata*. 

 In confirmation of the identity of the crystalline strata in the north 

 with the Silurian rocks of the south, we may mention the illustrative 

 fact that calcareous matter pevails most extensively towards the west- 

 ern extremity of both groups of rocks. In the Silurian strata at their 

 eastern termination near St. Abb's Head, no calcareous beds are 

 known ; they begin to appear in thin courses in Peeblesshire near the 

 centre of the chain, and are very abundant in Ayrshire. It is the 

 same with the crystalline strata. In the coast-section from Stone- 

 haven to Aberdeen, I have seen no calcareous bands ; in Forfarshire 

 and Perthshire several are known ; they become still more abundant 

 in the north of Argyllshire ; and in Cantyre we have, as just stated, 

 a great group of limestone rocks. 



If this analogy be sustained, it follows that the upheaval of these 

 strata has taken place soon after the deposition of the Lower Silurian 

 series, and that no new strata have been formed until near the close 

 of the Devonian or commencement of the Carboniferous epoch. In 

 this place, at all events, the upper old red sandstone and coal forma- 

 tion rest immediately on a mica-slate, which I conceive to be of Lower 

 Silurian age, the whole of the Upper Silurian and Lower Devonian 

 being omitted. The same order seems to prevail in the north and 

 west of Ireland, where, in some places, the red conglomerates and 

 coal-measures follow immediately on the mica-slate, in others on the 

 Middle or Lower Silurians. Hence the great break in the continuity 

 of the Scottish formations is between the Lower Silurian strata on 

 the one hand, and the Old Red Sandstone on the other f. 



I formerly pointed out the predominance in the mountain-chains 

 of Scotland of two great lines of elevation, the one running from 

 W.S.W. to E.N.E. , predominating in all the eastern and central por- 

 tions of the kingdom ; the other with a S.W. to N.E., or even more 



* See Sedgwick and Murchison on the Geology of Arran, Trans. Geol. Soc. 

 2nd ser. vol. iii. p. 21. 



t This may explain why Scottish geologists generally placed the division-line 

 between the Transition ( = Silurian) formations and the Secondary before the Old 

 Red Sandstone, and not subsequent to it as in other countries. 



