On the probable cause of the non-existence of deposits between the Permian and the Lower Silurian in the Southern Uplands of Scotland

The great Silurian district in the south of Scotland, named by Mr Geikie ‶the southern uplands of Scotland,″ presents the phenomenon of large patches of red sandstone of Permian age superimposed in a nearly horizontal position on the almost vertical Silurian rocks. This sandstone has been entirely worn away from the hills and extensive valleys by glacial and aqueous action; in other places less exposed to erosive forces patches of it remain; while in many of the narrower glens and gorges, where it has been comparatively protected from erosion, it has been left in masses of great thickness. The enormously lengthened Devonian and Carboniferous epochs which succeeded the upheaval of the underlying rocks have left no trace of their existence in this locality. This gap can only be referred to one of two causes—first, either all the Devonian and Carboniferous deposits have been removed by denudation between the period of upheaval and the Permian epoch; or, secondly, no Devonian or Carboniferous deposits ever existed in the district. Finding that there exists no evidence of ice action, which is the great agent in denudation, between the Silurian and Permian epochs, and that even granting great denudation during this period, it is highly improbable that all traces of the intervening deposits would be entirely obliterated had they existed, the author is driven to the hypothesis that no deposits ever existed in the district in question between the Silurian and Permian; and that, during the deposition of the Upper Silurian and Old Red Sandstone in other parts of the globe, the Lower Silurian of the southern uplands were high and dry above the sea. Between this epoch and the Carboniferous, the author conjectures that the Silurian rocks were slowly sinking, until during the Upper Carboniferous period they were once more completely covered by the sea. Then commenced the deposition of the Permian sandstone, which filled all the crevices and hollows, and which may have formed a thick crust over the whole of the underlying rocks. At a later period there ensued a movement in a contrary direction, and a slow horizontal rising took place,—not a violent upheaval like the former one,—but a gradual upward movement, until the old Silurian rocks, with their accumulated crust of sandstone, once more emerged from the sea. Then ensued the glacial epoch, which has left such extensive tokens of its presence, still further wearing down the hills and scooping out the valleys, from which it has been mainly instrumental in removing the deposit of Permian sandstone, leaving it only in narrow gorges and places protected from its action.