Sea cliffs are precipitous rock faces formed through erosion by the sea. Because the waves exert a powerful erosive effect against the rock closest to sea level, sea cliffs are frequently eroded into overhanging shapes. Because of this, it can usually be assumed that overhangs in sea cliffs reveal the high watermark of the sea. And if there is a series of overhangs in a cliff, we can infer that they represent different water levels as the sea rose and fell.
External link: http://fishfun.com.tw/en.php?node=feature&album_id=28