380 



THE GEOLOGIST. 



and Strathearn, including the south-eastern flanks of tlie Grampians for about 

 two-thirds of their course. Metamorphic rocks, trap-rocks, the Lower and 

 Middle members of the Old lied Series (the former being sandstone, and the 

 latter conglomerate), are the constituent rock-masses of the district, and give 

 it its peculiar physical features. The mode in which these rocks are associated 

 is well exhibited in the section on the coast (at Stonehaven), and in the several 

 sections in the interior where streams lay bare the rocks. Sections at Stone- 

 haven, Glenburiiie, Strathfinlass, North Esk, West Water of Lithnot, Cruick 

 Water, South Esk and Prosen, Blairgowrie, Dunkeld, Strathearn, and Glen- 

 artney, were described in detail. 



Against the nearly vertical, but somewhat north-westerly dipping, meta- 

 morphic schists (which sometimes include conformable limestones), come purple 

 flagstones, but usually separated from them by trap-rocks, having the same 

 strike. These flagstones pitch to the south-east, but retain a high angle away 

 from the schists, and, in many places, are intercalated with beds of trap. 

 The lower purple flagstones are unfossiliferous ; but higher up tracks of Crus- 

 t'dcesiiis CProtic'hmte.iJ have been discovered by the Rev. H. Mitchell. The 

 grey fossiiiferous flagstones of Eorfarshire succeed, still with a steep dip. 

 Conglomerates succeed, in beds having a less inclination, gradually becoming 

 more and more horizontal as they reach the low country. 



The axis of the elevation of the Grampians thus appears to be along their 

 southern margin, and to be marked by the trap-rocks separating the meta- 

 morphic schists and the purple flagstones of the Old Eed series, and giving the 

 latter their general south-easterly dip. As the metamorphic rocks of the Gram- 

 pians have not yielded any fossils, their relation to the other old rocks of 

 Scotland is difiicult to determine. 



3, " On the Old Red Sandstone of the South of Scotland." By Ai-chibald 

 Geikie, Esq., E.G.S., of the Geological Survey of Great Britain, 



This paper was the result of a series of explorations carried on at intervals 

 from Girvan to St. Abb's Head. The first part related to the geology of the 

 ])order-district of Lanark and Ayr, near Lesmahagow. The Silurians and 

 Lower Old Red sandstones of that district, as formerly pointed out by Sir 

 Roderick Murchison, form one consecutive series. Tliey are traversed by 

 great numbers of felstone-dykes, and are disposed in longitudinal folds, ranging 

 from north-east to south-west, the Silurian strata forming the axis of each 

 anticline. Both series are overlaid unconformably by Carboniferous strata 

 belonging to the horizon of the Mountain Limestone group of Scotland. The 

 features of this unconformity are well displayed all round Lesmahagow, where 

 an enormous series of Lower Old Red sandstones, more than ten thousand feet 

 thick, have their truncated edges overlapped by gently inclined beds of Car- 

 boniferous sandstone, shale, and limestone. The whole of the Lower Carboni- 

 ferous group and the upper Old Red Sandstone, amounting in all to at least 

 six tliousand or eight thousand feet, are here wanting. But as the junction of 

 the Carboniferous Limestone with the Lower Old Red is traced towards the 

 cast, tlie thickness of strata between the two formations gradually increases, 

 until at tlie Pentland Hills the whole of the Lower Carboniferous series and a 

 considerable part of the Upper Old Red have come in ; and these strata, as at 

 Lesmahagow, rest quite unconformably on the base of the Lower Old Red 

 Sandstone and the higher beds of the Upper Silurian. Hence it becomes 

 np]iarent tliat in tlio south of Scotland, as in Ireland, there is a great physical 

 hvvA bclAvecn the Upper Old Red Sandstone and the lower part of that 

 fui'uiaiiou. 



The author next pointed out the character of the Upper Old Red Sandstone 

 in East Lothian and Berwickshire ; showing that it graduated by imperceptible 

 stages into the Lower Carboniferous sandstones, and formed with these one 



