Sand grains are seldom blown in the wind, that would be a sand storm, rare in Scotland, more likely is the process of saltation is grains are lifted in the wind stream until gravity plays on them and they drop back onto the beach, hitting another grain, displacing it, which in turn is lifted along the beach.
So, sand is moved along a beach like this until it hits something, like a shell or a blade of grass. When we see this process, we see a constant stream of sand along the beach, tiny grains moving very fast, so it appears like a flow to us. Quite lovely to think one shell can make a huge dune.
Contributed by Countryside Ranger Ranald Strachan