Developments of arenaceous beds in different parts of North and Central Wales are shown to be contemporaneous and are grouped together as the Lower Ludlow Grits. Directions of transport based mainly on flute cast measurements are recorded. It is shown that the Welsh Basin was divided into two distinct troughs. In the northern, Denbigh Trough, greywackes were deposited by currents flowing from west to east. In the southern, Montgomery Trough, no greywackes are found, but calcareous siltstones were deposited by currents flowing from south to north. Turbidity current flow was along the lengths of the troughs. Contemporaneous slumping was down the sides of the troughs.