398 CHARACTER OF GROUNDS DIKED IN. 



and the Sclielde bring down large quantities of fine earth. The 

 prevalence of west winds prevents the waters from carrying this 

 material far out from the coast, and it is at last deposited north- 

 ward or southward from the mouth of the rivers which contribute 

 it, according to the varying drift of the currents. 



Marme Deposits. 



The process of natural deposit which prepares the coast for 

 diking-in is thus described by Staring : " All sea-deposited soil is 

 composed of the same constituents. First comes a stratum of 

 sand, with marine shells, or the shells of mollusks living in 

 brackish water. If there be tides, and, of course, flowing and 

 ebbing currents, mud is let fall upon the sand only after the 

 latter has been raised above low-water mark ; for then only, at 

 the change from flood to ebb, is the water still enough to form 

 a deposit of so hght a material. Where mud is found at great 

 depths, as, for example, in a large proportion of the Ij, it is a 

 proof that at this point there was never any considerable tidal 

 flow or other current The powerful tidal currents, flow- 

 ing and ebbing twice a day, drift sand with them. They scoop 

 out the bottom at one point, raise it at another, and the sand- 

 banks in the current are continually shifting. As soon as a bank 

 raises itself above low-water mark, flags and reeds establish them- 

 selves upon it. The mechanical resistance of these plants checks 

 the retreat of the high water and favors the deposit of the earth 

 suspended in it, and the formation of land goes on with sui-pris- 

 ing rapidity. When it has risen to high-water level, it is soon 

 covered with grasses, and becomes what is called schor in Zee- 

 land, hwelder in Friesland. Such grounds are the foundation or 

 starting-point of the process of diking. When they are once 

 elevated to the flood-tide level, no more mud is deposited upon 

 them except by extraordinary high tides. Their further rise is 

 accordingly very slow, and it is seldom advantageous to delay 

 longer the operation of diking." * 



* Voormaals en Thans, pp. 150, 151. According to Reventlov, conferxxB 

 first appear at the bottom in slioal water, then, after the deposit has risen 

 above the surface, Salicornia Jierhmea. The 8alieornia is followed by various 

 £and-plants, and as the ground rises, by Poa distans and Poa ma/ritima and 



