Current bedding

Cross bedded sediments were deposited in shallow water where there were strong and variable currents. The cross bedding develops from the formation and movement of ripples. Sediment moves up the ripple and avalanches down the lee slope, see diagram. Ripples provide evidence of ancient current direction. They also tell you whether or not the stone has been laid in the wall upside down.

Reference Bath In Stone by Elizabeth Devon, John Parkins, David Workman