Along the Atlantic coast from the mouth of the Adour to the estuary of the Gironde there stretches a monotonous line of sanddunes bordered by lagoons on the land side, but towards the sea harbourless and unbroken save for the Bay of Arcachon.
Here the sea has greatly eroded the normal regular, harbourless line of the west coast of Africa, forming bold capes and numerous inlets or estuaries.
On still other parts of the coast a recent small elevatory movement has exposed part of the former sea bottom in a narrow coastal plain, of which some typical harbourless examples are found in Oregon.