52 SEA AND LAND 



which are the stron^;er because of the exposed position of 

 the slope. The sand whirls over the crest and falls into the 

 lea, where it is caught and fixed by the vegetation so that the 

 less powerful winds which assail it on that side cannot stir it 

 from its position. This process repeated may advance the 

 dune into the interior at the rate of several feet a year. For 

 a time it receives constant accretions of material from the 

 neighboring shore ; but as it departs from the coast these 

 contributions become less in quantity ; generally another dune 

 forms behind the first of the train, and absorbs all the sand 

 which is blown from the beach. As the moving mass passes 

 into the interior it usually becomes ever more and more 

 coated by vegetation, for the reason that it comes into a 

 region where a greater variety of plants can dwell than upon 

 the shore-lands ; moreover the sand becomes decayed, tends 

 to cement into a firmer shape, and provides more nutrition 

 for the growth of vegetation. Thus in time the dune is 

 brouirht into the state of an immovable hill, becomes orass 

 or forest clad, and only rarely and to the trained eye reveals 

 its curious origin. 



On the small islands which frequently border the shores 

 of the great lands in the manner in which they are distributed 

 alono" the northern coast of the United States, beaches are 

 rare. Only here and there do we find points where the softer 

 character of the shore materials has permitted the sea to 

 form an indentation into wliich the waste from the neighbor- 

 ing shores is driven by the waves, and there retained until 

 the movement impressed on the fragments by the surges has 

 ground them to powder, which the undertow and other cur- 

 rents can carry out to sea. The result is, that the greater 

 part of the waste from island shores is likely to be carried 



