As an erosive force, water rules the Earth, surpassing junior partners wind and ice. Hour by hour, eon by eon, the oceans and rivers turn great mountains into mere grains of sand. This handiwork is on full display at the base of rocky coastal cliffs the world over, where daily tides burrow into the Earth’s stony foundations. The burrowing gradually undermines the cliff at a place called the wave-cut notch. Eventually, whole sections collapse. The cliff face slowly retreats as a result, extending landward the edge of a gently sloping underwater platform of wave-cut debris whose seaward edge, which might lie far beyond the breaker zone, marks the point where ocean waves ﬁrst started eroding the cliffs. Sublime examples of wave-cut platforms can be found in western Newfoundland and at Pebble Beach near Arcata, California.