Coastal erosion at work.
On the far side of the cove and at the top of the cliffs can be seen what were the landward ramparts of Crane Castle, neolithic (and more recent) fort. The gap between the ramparts and Crane Islands is the site of what was by all inferences a sizeable settlement. The far cliffs would not have been visible in those days from this position.
Many headlands had forts and settlements and many of those have completely disappeared.