On the Association of the Lower Members of the Old Red Sandstone and the Metamorphic Rocks on the Southern Margin of the Grampians

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Abstract
T he area to which this paper referred is the tract lying between Stonehaven and Strathearn, including the south-eastern flanks of the Grampians for about two-thirds of their course. Metamorphic rocks, trap-rocks, the Lower and Middle members of the Old Red 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 Stonehaven, Glenburnie, Strathfinlass, North Esk, West Water of Lethnot, Cruick Water, South Esk and Prosen, Blairgowrie, Dunkeld, Strathearn, and Glenartney, were described in detail. Against the north-westerly dipping metamorphic 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 Crustaceans ( Protichnites ) have been discovered by the Rev. H. Mitchell. The grey fossiliferous flagstones of Forfarshire 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 metamorphic schists and the purple flagstones of the Old Red series, and giving the latter their general south-easterly dip. As the metamorphic rocks of the Grampians have not yielded any fossils, their relation to the other old rocks of Scotland is difficult to determine.

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