Maritime and Peat Soils 59 



often difficult or impossible to obtain any direct evidence 

 as to the natural vegetation of such soils because they are 

 generally extremely fertile, and entirely under cvdtivation 

 or in permanent pasture. In the neighbourhood of great 

 cities, which are frequently situated on the flood plains 

 of the lower courses of big rivers, these rich alluvial soils 

 are extensively used for market gardening. 



Travelling seawards down the course of such a river, 



we pass from the plain of river alluvium to 



„ the salt mud associated with the tidal estuary. 



The natural vegetation is halophilous (p. 332), 



but when the tide is kept out by sea walls, and the land 



is drained, it makes admirable pasture. " The Marshland," 



occupjruig the northern (seaward) portion of the old 



estuaries of the Ouse, Xen, Welland and Witham and 



lying round the Wash, their common estuary, now much 



reduced in size, is the most extensive area of this kind in 



the country. 



Blown sand, forming sand-dunes, which support a very 

 characteristic vegetation (p. 339), occurs wherever a con- 

 stant supply of sand is thrown up by the sea above 

 highwater mark, and thus comes under the action of the 

 wind. 



Shingle or pebble beaches thrown up above high- 

 tide mark also have a vegetation of their own, allied to 

 that of sand-dunes but with distinct characters. The 

 best known and most extensive are the Chesil Bank 

 in Dorsetshire, Dungeness in Kent, and Orfordness in 

 Suffolk. 



Finally, among recent deposits, we have the sharply 

 characterised organic soils of which the 

 Peat soils. ^^^^ ^^^j^^ formed where vegetable remains 



accumulate in the presence of water and with deficient 

 oxidation (p. 35), are by far the most important. The 

 kind of peat formed on the edges of water comparatively 

 rich in mineral salts is often accumulated in the upper 



