SALT MAESHES-PAST AND FUTURE 



be floated in a tumbler of water. The slight- 

 est touch of a grass blade or a cat's paw of 

 wind sends the sand to the bottom. In winter, 

 ice cakes, with mud and sand frozen into their 

 lower surfaces, or bearing loads broken away 

 from the banks, are often stranded far afield 

 by the high winter tides, and, in melting, ma- 

 terially help in the building up of the marsh. 

 A certain amount of sand is blown inland 

 over the marshes from the dunes. 



The fourth zone of vegetation, the zone of 

 the black grass, which fringes the whole re- 

 gion, is visited only by the exceptionally high 

 tides, and very, very slowly creeps up on the 

 fresh water land, displacing the life there, be 

 it fragile herbs or mighty forest trees. All 

 yield before the strength of the salt sea. It 

 has been found that one and a half per cent, 

 of common salt in the soil is poisonous to 

 plants that do not naturally grow on the sea- 

 shore, while sea water contains two and a half 

 per cent., and the soil of salt marshes, on 

 which all these halophytes, or salt-loving 

 plants, grow, may contain even more salt. 



In other words, the vegetation of all the 

 zones holds its own, and in places more than 

 holds its own against ,the advancing sea. A 



219 



