Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/176

132 Still more striking is the other phenomenon I have alluded to as confirming the existence of the great faults in question. As has already been pointed out, the highest mountains in the south-east of Sutherland are capped by the beds of the Lower Old Red Sand-stone and Conglomerate, which, as we follow them towards the north, are found dipping under the enormously developed strata of calcareous and bituminous flagstones with associated sandstones, marls, &c. constituting the Middle Old Red Sandstone, and occupying so large a portion of the county of Caithness. Now no geologist can for a moment glance at the present relations of these strata without perceiving what Sir Roderick Murchison so clearly pointed out — namely, that the various patches of Old Red Conglomerate and Sandstone are the remaining vestiges of a widely spread formation which was doubtless once covered by deposits of Middle Old Red Sandstone age, forming the connexion between the great fish-bearing beds of Caithness and Ross. Hitherto, owever, not a trace of the Middle Old Red or Caithness Schists had been found in the county of Sutherland. During my examination of the district, I had the good fortune to discover a small but well-marked patch of these strata, the position of which was such as to be absolutely inexplicable on any hypothesis but that of the existence of great faults, and to afford the very strongest support, I may say the most triumphant confirmation, of those conclusions as to the relations of the strata which have been deduced from other facts.

The section which best illustrates the position and relations of the fragment of the Caithness flags referred to is exposed in the Allt-gharashtiemore (Gartymore Burn), north of the village of Port Gower; but other less complete sections enable us to trace the extent of this singularly isolated patch of the Middle Old Red Sandstone, and to show that it is about five miles long and from a quarter of a mile to half a mile broad. The accompanying section (fig. 13) clearly illustrates the relations of this wonderfully preserved fragment of a great formation. It is evidently enclosed between two great faults, by one of which it is brought into apposition with the granite of the Ord, which is probably of Lower Silurian date, while, by the other, strata of Upper Oolite age have been let down against it. The wellmarked and highly distinctive characters of the beds of the Caithness Schist leave no room for doubt as to the correctness of the identification of the strata of this isolated patch. The Rev. J. M. Joass, who kindly examined this section with me, and whose intimate acquaintance with the Old Red Sandstone of the north of Scotland gives such weight to his opinion on the subject, informs me that he has not the slightest hesitation in considering them part of the Middle division of that formation, and that he has little doubt they belong to the lower part of that division. The strata, as might be expected from their position between the two great faults, are greatly disturbed and crumpled. They are seen again, but more