OF SAND FORMATIONS ON MARINE COASTS. 33 



and depressions, that governs the development of such embryonic sand 

 hills into a dune complex. In almost every case the latter formation 

 has had such origin from a number of nuclei, while a dune massiv is 

 formed from a single embryonic dune. 



If the plants should not influence the development of dunes the 

 ridges would, like large waves, roll over the land until they were 

 stopped either by water or by high mountains. In most cases it is the 

 plants wliich have caused the broken forms of the sea coast dunes. 

 Inland dunes have, as a rule, a more regular shape. 



There is no other geological formation of the present time which 

 is the result of such a combination of factors from the organic and 

 inorganic nature. Dunes are developed wherever the winds can play 

 over the loose sands, and as soon as the sand begins to drift, tire 

 ordinary vegetation is destroyed and plants which thrive in drifting 

 sand immigrate, and thus begins the co-operation between the drift 

 sand and the dune plants, the result of which is the dune. Although 

 there is a struggle for power between the moving sand and the plants, 

 it is remarkable with this strife that they both thrive best where they 

 are almost of equal strength. If the plants have gained a victory they 

 will soon be replaced by other plants, and then it can happen that the 

 wind again breaks open the soil and the sand starts to drift afresh. 



SAND FIELDS NEAR THE COAST. 



As long as an obstruction has caused the formation of a dune, one 

 of these will act as a recipient for the sand, and in this way dunes after 

 dunes are formed until finally a whole sea of sand covered with dunes 

 is formed. 



The encroachment of dunes is due not only to the travel of the duues 

 themselves, but also to the formation of new dunes to the leeward from 

 material supplied by the sand shower. 



In some cases, however, when the dunes have not been fixed by a 

 vegetation, the sand skims along the surface like snow drifting before a 

 stiff breeze and accumulates rapidlj', covering the plains without forming 

 any hills. Further, the fine material which has been lifted to a certain 

 height in the air, is deposited behind the dune region, and is quicklv 

 covered with vegetation, as it offers better condition for plant life on 

 account of its greater coherence and capacity of retaining moisture 

 than the coarser dune sand. These sand fields sometimes cover con- 



