A Flandrian [Quaternary] marine terrace forms the coastal zone between Biarritz and Hossegor [west coast of France]. It is bordered on the east, between the Adour and Ondres, by Pliocene hills, but farther north, next to outcrops of the Landes sands, by typical parabolic dunes. This terrace, averaging 2 km in width and 20 to 30 m in thickness, rests on a Tertiary substratum. It is composed of sands, gravels, and small pebbles as well as fluviomarine silts. The macrofauna recovered comprises modern littoral forms. Post-Flandrian eolian deposits cover it.