284 THE EARTH'S SURFACE AND PLANT LIFE 



Almost no plant life can find lodgment in these shifting 

 sand piles, and so the wind continually finds loose sand on 

 which to act, and a dune country is always a region of 

 shifting sands. As the dunes move in the direction of 

 the prevailing wind they sometimes invade a fertile coun- 

 try, so that it becomes necessary if possible to find a way 

 to check their movement. This has been done in some 



places by planting certain 

 kinds of grasses capable 

 of growing in the sand 

 and thus protecting the 

 FIGURE 92 sand particles from the 



action of the wind. 



Sand dunes are found along almost all low sandy coasts, 

 and they render difficult the building and maintenance of 

 roads and railroads to many beach towns. 



Wind-borne Soils. Whenever the wind blows over 

 dry land, particles of dust and sand are blown away and 

 deposited elsewhere. The interiors of our houses often 

 become covered with dust blown from the dry streets. Even 

 on ships at sea, thousands of miles from land, dust has been 

 collected. 



In volcanic eruptions great quantities of dust are thrown 

 into the air and spread broadcast over the earth. On the 

 highest and most remote snow fields particles of this dust 

 have been found. In the great eruption of Krakatoa, dust 

 particles made the complete circuit of the earth, remaining 

 in the air and causing a continuance of red sunsets for 

 months. 



Sand is not carried so far as dust, but at times of strong 

 wind it is often borne for long distances. Even houses, 



