132 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 8, 



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 occu- 

 pying so large a portion of the county of Caithness. Now no geo- 

 logist 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 Conglo- 

 merate 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, however, 

 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, 1 had the good fortune to discover a small but well-marked 

 patch of these strata, the position of which was such as to be abso- 

 lutely 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 illus- 

 trates 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 well- 

 marked and highly distinctive characters of the beds of the Caith- 

 ness Schist leave no room for doubt as to the correctness of the iden- 

 tification 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 



■ * Vide Murchison, Quart. Journ. Geol. Soc. vol. xv. (1859) p. 393 et seq. 



