24 GENESIS AND DEVELOPMENT 



shore which is continuously moistened by the spray from the sea, and 

 it may even occasionally become inundated. The sand of this formation 

 which has been piled up by the waves, is picked up by the wind and 

 carried inland. It is usually of a light color. The upper layers are 

 rapidly drying up, but the ground water keeps at a high level, and 

 moisture is usually found at a very slight depth. 



The upper beach is limited on one side bj' the line of debris that 

 marks the highest water. This debris, cast up by the sea, consists of 

 lumber and other wooden articles, fruits and seeds, fragments of marine 

 plants, and a quantity of animal remains, rapidly decaying. The upper 

 beach is also characterized by a greater rise in elevation and contains 

 more organic matter than any other part of the beach. The development 

 of this formation is modified to a greater extent by the wind than by 

 water, and it is especially on this strip of the shore, where the sands 

 co m mence to drift, and where they usually form the first ridges of sand 

 parallel to the coast, which we know as dunes. 



The windmade embaniments on the beach have a remarkable con- 

 struction, somewhat diiferent from the usual. When the shifting of the 

 sand is very rapid, the littoral dunes do not reach any remarkable height, 

 and their existence is then very precarious. 



DUNES. 



The etymologv' of the word dune is somewhat obscure. Generally 

 it is presumed that it is derived from the Celtic word dun, hill. In 

 Latin it is called dunum, in Greek howov, and hence the modern lan- 

 guages have acquired the use of the same term in more or less changed 

 dress. According to Grewingk, not every ridge of sand parallel to the 

 coast is a dune, as they can in some cases originally be sand-banks formed 

 under water, which later have been lifted above the surface of the water 

 through the elevation of the shore. Dunes are formed especially where 

 the sands are almost purely siliceous, and hence incoherent, and little 

 fit for any kind of vegetation. They reach their greatest height on 

 projecting coasts that receive the winds from different directions. 



The source of the dune sand is usually either diluvial sand, which 

 has been laid bare, or sand which has been brought ashore by the sea. 



On the Dutch and Danish west coasts almost all the sand which 

 forms the dunes traces its origin from the sea. It is here thrown up 

 on the beach hy the waves, and as soon as it has been dried by the sun. 



