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COCKS, L. R. M., PRICE, D. 1975. The biostratigraphy of the upper Ordovician and lower Silurian of South-west Dyfed, with comments on the Hirnantia fauna. Palaeontology, 18, 4, 703–724.
L. R. M. Cocks and D. Price Late Ordovician and early Silurian beds around Haverfordwest, South-west Dyfed (Pembrokeshire), Wales, are remapped and their faunas reviewed. Five formations are defined, representing a fairly continuous succession from mid Ashgill (Cautleyan) to late Llandovery (Telychian). New faunal evidence places the local Ordovician-Silurian boundary higher than has been previously suggested, within the Haverford Mudstone Formation. The world-wide late Ashgill Hirnantia fauna is reviewed, and the conclusion reached that it represents a diachronous animal life assemblage and that it need not necessarily represent the latest local Ordovician fauna. The Palaeontological Association (Free Access)