TEXTº There is great variation among shorelines, for they are created by different forces. Some are fairly ancient (although still young in geological terms); others are the products of sand brought by currents or a new lava flow. There are three kinds of shorelines along the Atlantic: piedmont which is part of the ancient continent; coastal alluvium, which consists of sediments carried down by rivers and washed in from the sea; and the edges of old mountains. It is clear that rocky bluffs plunging into the ocean are the edge of an extremely old land mass, while a sandy barrier island consisting of little more than a wide beach may not even appear on early navigational charts.In geological time, a shoreline is an ephemeral margin, which, over centuries and millennia, migrates back and forth according to climatological and geological events. During glacial epochs, when enormous quantities of water are locked up in polar ice caps, the sea level is lower and more land is exposed. In interglacial periods, the ice masses at the poles melt, liberating water into the oceans and flooding coastal plains and even penetrating far inland over low-lying continents. The life of seashores - plant or animal: burrowing, attached, or motile - must migrate with the coastline.There is great variation among shorelines, for they are created by different forces. Some are fairly ancient (although still young in geological terms); others are the products of sand brought by currents or a new lava flow. There are three kinds of shorelines along the Atlantic: piedmont which is part of the ancient continent; coastal alluvium, which consists of sediments carried down by rivers and washed in from the sea; and the edges of old mountains. It is clear that rocky bluffs plunging into the ocean are the edge of an extremely old land mass, while a sandy barrier island consisting of little more than a wide beach may not even appear on early navigational charts.
