Correlation of the Achanarras and Sandwick Fish Beds, Middle Old Red Sandstone, Scotland

Abstract

The Achanarras Fish Bed of the Middle Old Red Sandstone of Caithness, separating the Lower and Upper Caithness Flagstone Groups of Donovan, Foster and Westoll (1974), has long been correlated with the Sandwick Fish Bed of Orkney which lies between the Upper and Lower Stromness Flags. The remarkable similarity of the fish faunas, in terms of species present, has hitherto been marred by the absence in Orkney of Palaeospondylus gunni which is abundant at Achanarras. This note records a single specimen of P. gunni in the Sandwick Fish Bed in the quarry on Cruaday Hill, Quoyloo. [HY 246 217], (Nos. 10579 and 10580; Palaeontology collection of Aberdeen University). The general correlation of these fish beds has been apparent and useful for many years (Westoll 1951; Miles and Westoll 1963), and although the finding of P. gunni in Orkney considerably strengthens this correlation, there remains the fact that the various species occur in markedly different abundances in the two areas. Osteolepis is abundant in Orkney and rare at Achanarras, whilst the converse is obviously true of Palaeospondylus. Rayner (1963), using information supplied by Professor T. S. Westoll, published a generalised range and abundance chart for the fish at Achanarras, where the most notable feature is the abundance of Dipterus near the base of the fish bed, in smooth black flags. Coccosteus occurs in the upper part of the bed and, despite extensive collecting, I have yet to see Dipterus and Coccosteus on the same bedding plane. Palaeospondylus is occasionally found associated . . .