98 GEOLOGY 



When dunes migrate into a timbered region, they bury and kill 

 the trees (Fig. 59). In one instance on the coast of Prussia a tall 

 pine forest, covering hundreds of acres, was destroyed during the 

 brief period between 1804 and 1827. 1 At some points in New 

 Jersey orchards have been so far buried within the lifetime of 

 their owners that only the tops of the highest trees are exposed. 



Fig. 59. Lee side of a sand dune, Cape Henry, Va. The dune is advancing 

 on a forest and burying the trees. (Hitchcock.) 



Trees and other objects once buried may be again discovered by 

 farther migration of the sand (Fig. 60) ? 



Distribution of dunes. Dunes are likely to be developed wher- 

 ever dry sand is exposed to the wind. They are especially char- 

 acteristic of the dry sandy shores of lakes and seas, of sandy valleys, 

 and of arid sandy plains. 



Along coasts, dunes are likely to be extensively developed only 

 where the prevailing winds are on shore. Thus about Lake Mich- 

 igan, where the prevailing winds are from the west, dunes are abun- 

 dant and large on the east shore, and but few and small on tho 

 west. Along valleys, dunes are usually on the side toward which 



1 Merrill. Rocks, Rock Weathering, and Soils, p. 295. 



2 Cowles. The Ecological Relations of the Vegetation of the Sand Dunes 

 of Lake Michigan. Botanical Gazette, Vol. XXVII, 1899. An excellent 

 study of the relations of sand dunes and vegetation. 



