Figure 20.1Coastlines exhibit a variety of geologic forms. (a) Long, straight, sandy beach, Pea Island, North Carolina. (b) Rocky coastline, Mount Desert Island, Maine. This formerly glaciated coastline has rebounded since the end of the last ice age, about 11,000 years ago. (c) The Twelve Apostles, Port Campbell, Australia, a group of stacks that developed from cliffs of sedimentary rock. These remnants of shoreline erosion are left as the shoreline retreats under the action of waves. (d) Coral reef along the Florida coastline.