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The Use of Gryphaea in the Correlation of the Lower Lias

  • A. E. Trueman (a1)

In the course of recent investigations in the littoral Lias of South Wales and parts of Somerset the writer has frequently found that almost the only fossils in some of these deposits are species of Ostræa and Gryphæa, which occur in regular sequence and are of considerable value in correlation. On consulting the literature describing these genera it became apparent that the specific names have been frequently misapplied. From correspondence with other students of Liassic rocks it also appeared that there is some difference of opinion concerning the precise horizons at which such species are to be found.

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page 256 note 1 Hatch, , “The Boulder Beds of Ventersdorp, Transvaal”: Trans. Geol. Soc. S.A., vol. vi, 1903, p. 95.

page 256 note 2 Molengraaf, , “A hitherto unrecognized Formation underlying the Black Reef series”: Trans. Geol. Soc. S.A., vol. vi, 1903, p. 68.

page 257 note 1 See Jackson, R. T., “Phylogeny of the Pelecypoda: The Aviculidæ and their Allies”: Mem. Boat. Soc. Nat. Hist., vol. iv, 1890, p. 317. Kitchin, F. L., “Summary of Progress”: Geol. Survey, 1911. Davies, A. Morley, An Introduction to Palæoniology, 1920, p. 89.

page 257 note 2 See, for example, Hébert, M., “Observations sur les Gryphées du Lias, etc.”: Bull. Soc. Geol. France., ser. II, vol. xiii, 1855, p. 213; and Terquem, O., “Palénntologie de l' Etage Inférieur de la Formation Liasique, etc.”: Bull. Hoc. d'hist. nat. de. la Moselle, ser. II, vol. v, 1855.

page 257 note 3 Jones, John, “On Cryphsea Incurva and its Varieties ”: Proc. Cottes. Nat. Club, vol. iii, 1865, pp. 8195.

page 257 note 4 Buckman, S. S., “Jurassic Chronology: I. Lias”: Quart. Journ. Geol. Soc., vol. lxxiii, 1918. p. 274.

page 257 note 5 Tutcher, J. W., ibid., pp. 278–81.

page 260 note 1 Thompson, D'arcy Wentworth, On Growth and Form, 1917, p. 531.

page 261 note 1 Among Liassic Gastropoda, and some families of Ammonites, it is not uncommon to find adult specimens at the same horizon at somewhat different stages of evolution; some are more “highly accelerated” than others. The differences between the Gryphaeas, however, are much more apparent.

page 262 note 1 The very curved forms from the angulata zone generally differ from G. incurva in having a feeble sulcus (if any) and a larger area of attachment. They are, therefore, accelerated in some characters only.

page 264 note 1 The parallel evolution of these numerous series, each passing almost inevitably through comparable stages, and following what may be regarded, as a pre-determined “programme”, affords an example of what Dr. F. L. Kitchin has called “programme-evolution”. (See Lang, W. D., Catalogue Cret. Bryozoa, vol. iii, 1921, p. xviii.)

page 265 note 1 As in the type of G. incurva.

page 265 note 2 Lang, W. D., Catalogue of Cretaceous Bryozoa, vol. iii, 1921, p. x.

page 265 note 3 Jackson, R. T., loc. cit., p. 312.

page 266 note 1 Trueman, A. E., “The Liassio Rocks of the Cardiff District”: Proc. Geol. Assoc., vol. xxxi, 1920, p. 102.

page 266 note 2 Vaughan, A. & Tutcher, J. W., “The Lias of the Neighbourhood of Keynsham”: Proc. Brist. Nat. Soc., N.S., vol. x, 1903.

page 268 note 1 Richardson, L., “The Section of Lower Lias at Hock Crib, Fretherne, Glos.”: Proc. Cuttes. Nat. F.C., vol. xvi, 2, 1908, pp. 135–42.

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Geological Magazine
  • ISSN: 0016-7568
  • EISSN: 1469-5081
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