(Russian marshi; from the German Marsch), a low-lying zone of the seacoast that is flooded during the greatest high tides or during surges of seawater. They are usually composed of silt or sand-silt deposits on which humus-rich soils form. They ordinarily stretch in a band (generally not more than 30 km wide) that frames the tidal marshes, which, unlike coastal marshes, are subjected to the regular influence of high tide and ebb tide. They are sometimes below sea level, being separated from the sea by a strip of dunes. Coastal marshes are typical of the coast of the North Sea and are found in the Netherlands, Federal Republic of Germany, Great Britain, Denmark, and France, as well as in the eastern and southern United States. In the USSR the laida, which are common along the seas of the Arctic Ocean, are analogues of coastal marshes. In their natural state they are usually covered by highly productive meadows, which are often used for agriculture.