V.—On the Arenig and Llandeilo Groups

Abstract

The lower strata of the Silurian system are, as yet, but little known. The labours of Welsh and other geologists have brought to light the large fauna of the Lingula flags; but while the Upper Cambrian has thus been established and elucidated, the beds which lie immediately above it, namely the “Arenig group,” and the Llandeilo flags, remain to be searched, and a great part of the respective fauna of each to be described.The Areing, or Skiddaw, group of Sedwick forms the base of the true Silurian rocks; it immediately underlies the Llandeilo flags, from which it is totally distinct, although caused with them in Murchison's “Siluria.”