Traction – The rolling of boulders and pebbles along the sea bed by the force of the waves
The tractor (traction) could just about roll the big boulder.
Traction differs from saltation in that the material moved by the flow of the sea does not lose contact with the seabed. Traction is the rolling of larger particles along the seabed.
Over time, these larger pieces of material are worn down. This process results in smaller particles which then become subject to saltation.