Article: The biostratigraphy of the upper Ordovician and lower Silurian of South-west Dyfed, with comments on the Hirnantia fauna

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.