Waves usually approach the beach from an angle, the water runs over the sand and recedes at right angles to the shore. As a result the sand carried by the receding wave is transported down drift of its origin. This is described as littoral drift and it is a major factor in determining beach configuration.
As a result of this, sand continues to be transported in one direction. It is southward in the case of the New Jersey Shore. Thus the northern tips of islands here tend to be eroded and will shrink unless replenished with sand, while the southernmost tips of islands are elongated. A historical examination of the shore shows that this indeed has happened.