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THE BALIGILL OUTLIER As you travel west out of Caithness on the A836 the landscape changes suddenly from the green fields which lie on the Old Red Sandstone to the acid moorland which covers the crystalline rocks which form the basement of the Old Red Sandstone. A few miles further on, the drab browns and russets give way again to welcome green at the scattered hamlet of Baligill This is a small outlier of the Old Red Sandstone. The earliest reference I can find in the literature is on page 397 of a paper given by Sir Archibald Geikie in 1877 - 78.(1) It remains something of a mystery that Sir Archibald appears not to have noticed that the rocks were fossiliferous; he normally had a good eye for detail. The first mention of the fossils is in Crampton and Carruthers(2), page 76, where they reported that Dr R.H. Traquair had determined the fossil fishes from this horizon to be: Thursius macrolepidotus, Coccosteus decipiens and Dipterus macropterus (cf Pentlandia macroptera). There is, however, some- thing very odd about this assemblage of fishes: Thursius macrolepidotus is confined to the Wick Flagstones, which are part of the lowest group of the Middle Old Red Sandstone of Caithness, Coccosteus decipiens (cf cuspidatus) appears to be confined to the Achanarras Horizon which lies above the Wick Flags, and Pentlandia macroptera is typical of the John o' Groats Sandstones which lie at the upper end of the Middle Old Red. There were clearly only two viable conclusions to be drawn from this: either all three horizons were present at Baligill or Dr Traquair was mistaken in his classification of these fishes. I accordingly undertook, on the suggestion of Dr Waterston of the Royal Scottish Museum, to investigate the problem. The fishes I found there were classified by me as Osteolepis macrolepidotus, Coccosteus cuspidatus and Dipterus valenciennesi. This is a consistent group and typical of the Achanarras Horizon. I also had a bonus in that I found Cheirolepis trailli, also typical of the Achanarras Horizon. There was no evidence of any overlap since only one fish bed was involved. Fossil fishes also occur near the foot of the cliff at the eastern end of Strathy Bay. It is impossible to confirm that this is the same fish bed as the one at Baligill. If it were possible to view the coastal section from the sea it might be possible to extrapolate how the laminite containing the fishes develops towards the east. It is, in any case, impossible to collect material from the foot of the cliff, so it is unlikely that Traquair's material came from this locality. It would be surprising if this were to be the last word on this subject: something is always coming out of the Old Red to either confirm or refute earlier evidence. At a later date I found one very poor specimen of what appeared to be Palaeospondylus gunni at Baligill. This is only found in the Achanarras Horizon. And, in 1990, a couple of collectors, not realising that Baligill was scheduled now as a Site of Special Scientific Interest, collected a large fish which they did not recognise. I was shown this: it was Gvroptychius agassizi, also restricted to the Achanarras Horizon. At Achanarras itself Osteolepis, Cheirolepis and Gyroptychius are very rare, whereas in the Sandwick Fish Bed in Orkney they are common. It might be fair to presume, therefore, that the Baligill outlier should be equated with the palaeoecology of the Orkney rather than the Caithness horizon. The correlation between the fossiliferous localities in the Old Red Sandstone of the Orcadian cuvette, and which are based on fossil evidence is given in Table 1. REFERENCES
Jack Saxon |
