ELEMENTS OF GENERAL SCIENCE 



In some regions the winds build dunes, or hills, of sand, 

 those of coarsest sand near the shore and those of finest sand 

 farthest away. Some of these dunes may keep moving inland 

 (fig. 110) as sand from the windward side is carried over and 

 dropped on the leeward side. A dune may thus migrate far 

 inland, and with a change of prevailing winds it might mi- 

 grate back to the shore or even into the lake or ocean. Some- 

 times vegetation gains a foothold on a dune, and plants may 



FIG. 110. A group of sand dimes 



Trees, grasses, and other vegetation assist in accumulating and retaining the sand 



upon the dunes 



live upon it for ages ; then winds may again bring sand to 

 the dune, cover the vegetation beyond the tops of the tallest 

 trees, and later uncover all, and even remove the dune upon 

 which they stood. A visit to dunes will usually enable you to 

 gain some new notion of the wind as a factor in moving soils. 

 In some of our Western states, as Kansas and Nebraska, 

 there are wide stretches of sandy soil which in some places 

 forms dunes. On some of the cultivated land great annoyance 

 is caused by the soil blowing when it is fresh plowed ; at times 

 the soil drifts along fence rows much as snow drifts in winter. 



