562 PEHR OLSSON-SEFFER 



ally we meet, however, with a level beach of a varying width, and then 

 the coastal dune rises slowly at an angle varying from 4-16° on the 

 wind side. Its height varies on different coasts according to the 

 supply of material and the prevaiUng direction of the wind. 



On very long, straight, and open coasts the wind strikes the sand 

 over a long distance with the same force and under almost identical 

 conditions. On such coasts we find long stretches of dunes showing 

 a little diversified topography. As a rule the dunes are very little 

 curved and run at right angles to the direction of the wind. 



The diurnal variation of direction and force of winds which always 

 is considerable on marine coasts exercises some influence upon the 

 development of the drift-sand formations. The angle of deflection 

 from the direction of the annual wind resultant differs in summer and 

 winter, and from observations of these meteorological data in a 

 locality with drift sands it is possible to calculate to some extent as 

 to the annual movement and changes of the sand formations. 



Usually the downward eddy behind the coastal dune sweeps over 

 the stretch of land immediately following, and regular dunes are not 

 formed before some distance from the coastal dune. These first 

 dunes are formed round some obstacle, and their form is usually oval, 

 pointing toward the wind and the coast, but sometimes crescentic, 

 and convex to the wind. These small advance dunes are followed 

 by trains of large dunes, nearly uniform in shape. The wind sweeps 

 with brisk velocity upward along the gentle gradient and carries the 

 sand to the brink where it is deposited on the steep lee-side which is 

 further increased by the undercutting of the eddy. 



Beyond the reach and influence of the strong sea breeze the dunes 

 are more irregular, and lateral inequalities are formed connecting the 

 various individual dunes into long ridges. These travel forward in a 

 continuous march, slowly but surely. The form and location of the 

 drift changes gradually. 



A dune region shows a more or less undulating surface, which 

 suddenly may be broken up into quite high hills or ridges. Some- 

 times, when the forward march of the dunes has been stopped the 

 dune belt is continued inland in a gently undulating sand field. 



In a dune region many different stages of dune development are 

 observed, from the embryonic living dune to the large established 



