Reptiliferous Sandstone) in the county of Sutherland are such as to prove that these strata are of Secondary age, and that they are older than the Lower Lias.
I have argued this question hitherto mainly on stratigraphical grounds, and have shown that there would be the strongest reasons for believing the formation in question to be of Secondary age, even if there were a total absence of all palaeontological evidence.
But this is very far from being the case. The interesting descriptions of Stagonolepis, Telerpeton, and Hyperodapedon by Professor Huxley, and his discussion of their bearing on the age of the Reptiliferous Sandstones of Elgin are too fresh in the minds of all geologists to need recapitulation here. In 1858 Professor Huxley declared* that the palaeontological evidence in favour of the Secondary age of the reptiles was so weighty as to " lead one to require the strongest stratigraphical proof before admitting the palaeozoic age of the beds in which they occur." Since that date he has, as every one is aware, greatly strengthened that palaeontological evidence by demonstrating that, alike in Warwickshire, Devonshire, and India, Hyperodapedon occurs in beds of Triassic age†.
Thus we find that the stratigraphical and the palaeontological evidence with regard to this interesting formation in the north-east of Scotland are in complete accord, and we are justified in regarding it as of undoubted Triassic age — a fact which is of the greater interest from the circumstance that strata of that period are of such rare occurrence in Scotland.
Sir Roderick Murchison has suggested that, if the Reptiliferous Sandstones are to be referred to the Trias, they must in all probability be considered as representing the Keuper sandstones‡. In that case it may be consistent to place the " Cherty Rock of Stotfield " on the horizon of the lower part of the New Red marls. The partial break indicated by the overlying conglomerate beds, unattended as it is by any difference of dip, would be perfectly consistent with the absence of the higher portions of the Keuper series.
It was also pointed out by Sir Roderick § that there might be in Elginshire and Ross-shire an accidental conformity between beds differing as greatly in age as the Trias and Upper Old Red, and that on this supposition the apparent anomalies presented by the district might be accounted for. From a careful examination, however, of the whole question of the relations of the Primary and Secondary rocks around the Moray Firth, I am led to infer that the true key to the enigma presented by the Elginshire rocks is to be found in the great faults which certainly traverse the whole of the district, and as certainly have been the cause of even more striking pbenomena in other parts of it.
There are good reasons for believing that these Triassic strata of the north-east of Scotland are, like those of England (as has been
- Quart. Journ. Geol. Soc. vol. xv. (1859) p. 460.
† Ibid. vol. xxv. (1869) p. 138.
‡ Siluria, 5th edit. (1867) pp. 267, 268.
§ Ibid.
