130 Rev. A. Sedgwick and Mr. Murchison on Deposits contained between 



base of the figure may be represented by the old conglomerates, which range, 

 as before stated, from Port Skerry to the Ord ; and its vertex must be placed 

 on the shores of the Pentland Firth, among the masses of red sandstone which 

 compose the newest strata of the whole district*. The beds which form the 

 subsoil of the intermediate plains and morasses of the county, pass on their 

 north-eastern limits under the red sandstone of the Firth ; while, to the south- 

 west, they rise up to, and distinctly repose upon, the old conglomerates. From 

 this arrangement, it follows that the sections laid bare on the northern and on 

 the eastern coast, must exhibit the same order of superposition. The map* 

 will, however, show that the eastern side of the imaginary triangle is longer 

 than the other; a fact which is partly explained by the direction of the two 

 sections — partly by the greater expansion of the conglomerates in the neigh- 

 bourhood of the Ord — and perhaps still more, by some great dislocations which 

 have modified the arrangement of the intermediate system of beds on a part of 

 the eastern coast. 



We proceed to describe the several formations in the order in which we 

 examined them. 1st. In an ascending series from the lowest conglomerate of 

 Strathy Bay up to the newer sandstone of Dunnet Head. 2nd. From the 

 headlands of sandstone on the Pentland Firth in a descending series, down to 

 the conglomerates which rest against the granite of the Ord. 



Coast Section of Caithness. 



1st. Ascending Series fro^u Strathij-icater to the Upper Red Sandstone of the 



Pentland Firth. 



The secondary strata of Caithness are divided on the north-west from the 

 primary rocks of Sutherland by a small river called Strathy-water, which thus 

 forms their western limit. 



The lowest beds of the conglomerate are finely exhibited at the small fishing- 

 cove of Port Skerry, where they rest upon ledges of a compact red granite. 

 This conglomerate is almost entirely composed of fragments of granite and 

 quartz, united by a red-coloured argillaceous cement ; and, at the points of 

 junction with the granite, it is difficult to decide with precision where the un- 

 stratified crystalline rock terminates, and the depository beds commence. Some 

 varieties of this conglomerate contain much green earth. The superior beds 

 are here exposed in a low cliff of about thirty feet in height, and gradually 

 pass into a coarse-grained sandstone, which, in some of its lowest members, 

 exhibits an occasional pebble of granite. These again graduate upwards into 



* See Plate XIII. 



