Abstract
THE organic origin of Oldhamia has often been disputed. Originally described by Edward Forbes from specimens found at Bray Head, near Dublin, in rocks of the Cambrian formation, it has been found in a few other localities in Ireland, in rocks of a similar formation. In the dispute the weight of the evidence has seemed to be in favour of the views of Forbes, Jukes, Harkness, and Kinahan, that this lowly form is a fossil probably belonging to the Polyzoa, or to the Sertularian Polyps. So the matter has stood for a long time. A recent paper by Prof. W. J. Sollas, published in the Proceedings of the Royal Dublin Society for January last, once again opens the discussion. In the hope of throwing light on this problematical structure, thin slices for microscopic examination were cut, both parallel and transverse to its planes of cleavage. When these were placed under the microscope, all trace of the Oldhamia structure appeared to have vanished. An examination with the unaided eye showed, however, that it was still there, presenting itself as narrow, undulating, and branching bands of a lighter colour than the surrounding matrix. Its appearance, moreover, varied in an extraordinary manner according to the direction in which it was viewed. Looked at obliquely in a strong light, the thread-like bands are brilliantly illuminated, and appear faintly coloured with spectral tints; looked at directly, the bands become fainter, and are less clearly distinguishable from the matrix. In certain positions the slice taken at right angles to the bedding has an appearance somewhat suggestive of shot-silk, and, from the planes of cleavage, markings which remotely resemble in form the dendritic markings of Sutton stones extend into the surrounding matrix.
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On Oldhamia . Nature 35, 515–516 (1887). https://doi.org/10.1038/035515a0
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DOI: https://doi.org/10.1038/035515a0