Abstract
Summary: Sedimentary and volcanic rocks, now unrepresented in surface exposure, occur as xenoliths in the kimberlite of the Koidu District of eastern Sierra Leone. The sedimentary rocks prove, on micropalaeontological evidence, to have Lower Palaeozoic stratigraphic age. An eastern extension of the Ordovician/Silurian marine transgression on to the Leo Uplift of the West African Craton of some 200 km is indicated. The volcanic rocks may belong to the same cycle of surface rock generation or relate to the younger, widespread, Triassic magmatic event.