Abstract
CRUSTACEA IN THE OLD RED SANDSTONE.—The occurrence of eurypterid crustaceans of the genus Pterygotus in the Tilestones of Herefordshire and Worcestershire, and in the Old Red Sandstone of Forfarshire, has long been well known. These organisms have been regarded as characteristic of that section of geological time in the British area represented by the Ludlow and Lower Old Red Sandstone formations. Murchison used their presence in the Arbroath flagstones as an argument for placing these strata in his “Lower” division of the Old Red Sandstone, while on the other hand he argued from their absence in the Caithness flagstones and from the dissimilarity of the fishes, that these northern deposits must be of later age. He therefore classed the great flagstone series of Caithness and the Orkney Islands as “Middle” Old Red Sandstone, thus bringing this series of formations into correspondence with his favourite threefold classification of the Devonian system. Recently, however, in the first part of his memoir “On the Old Red Sandstone of Western Europe,” published in the Transactions of the Royal Society of Edinburgh, Prof. Geikie has pointed out that the contrast between the fish fauna of the Arbroath flagstones, or the ancient basin which he terms “Lake Caledonia” and that of the northern basin or “Lake Orcadie,” is by no means so marked as Murchison believed, and that the characteristic Pterygotus, on which the author of “Siluria” laid so much stress as an Upper Silurian and Lower Old Red Sandstone type, occurs on several horizons and at different localities in the Caithness and Orkney basin. An important discovery confirmatory of the extension of these Crustacea into the northern area has recently been made by Mr. James Linn in the course of the Geological Survey of Elginshire, now in progress. From the valley of the Spey he has obtained numerous fragments of what must have been a remarkably large Pterygotus, though the specimens so far found hardly admit of specific identification with the P. anglicus of Forfarshire. Pterygotus has thus been discovered in Orkney, Caithness, and on the Moray Firth, not only over an extensive geographical area, but throughout a wide vertical range of strata. These crustaceans must evidently have had a considerable and prolonged development in the waters of the northern basin of the Lower Old Red Sandstone period.
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Geological Notes . Nature 21, 241 (1880). https://doi.org/10.1038/021241a0
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DOI: https://doi.org/10.1038/021241a0