Llandovery Group

In geology, the Llandovery Group formerly referred to the lowest division of the Silurian period (Lower Silurian) in Britain. It was named after the town of Llandovery in Wales, although Charles Lapworth had proposed the name Valentian (from the Roman British province of Valentia) for this group in 1879. It included the Tarannon Shales (1000–1500 ft.), Upper Llandovery and May Hill Sandstone (800 ft.), Lower Llandovery, (600–1500 ft.)

The Lower Llandovery rocks consist of conglomerates, sandstones and slaty beds. At Llandovery they rest upon Ordovician rocks. These rocks occur with a narrow crop in Pembrokeshire, which curves round through Llandovery, and in the Rhayader district they reach a considerable thickness. They also occur in Ceredigion and Carmarthenshire.

The Upper Llandovery has local developments of shelly limestone (Norbury, Hollies and Pentamerus limestones). It occurs with a narrow outcrop in Carmarthenshire at the base of the Silurian, disappearing beneath the Old Red Sandstone westward to reappear in Pembrokeshire; north-eastward the outcrop extends to the Long Mynd, which the conglomerate wraps round. As it is followed along the crop it rests upon the Lower Llandovery, Caradog, Llandeilo, Cambrian and pre-Cambrian rocks. The fossils include the trilobites Phacops caudata, Encrinurus punctatus and Calymene blumenbachis; the brachiopods Pentamerus oblongus, Orthis calligramma and Atrypa reticularis; the corals Favosites and Lindostroemia; and the zonal graptolites Rastriles maximus and Monograptus spinigerus.

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