EOLIAL OR WIND-LAID DEPOSITS 



55 



Even villages and forests cannot withstand the advance of sand 

 dunes. The usual height is from ten to thirty feet, but some have 

 been found 300 feet high. Through some temporary change in 

 climate, as increased rainfall or diminished wind velocity, vegeta- 

 tion may start on the sand and gain such a foothold that the dune 

 becomes fixed or permanent. This fixed feature is sometimes 



Fia. 49. Sand dune advancing over forest, Beaufort Harbor, N. C. (U. S. Geol. Survey.) 



Fio. 50. A resurrected forest, Dune Park, Tni!i:inn. (Chamberlain and Salisbury, Cour- 

 tesy Henry Holt <fc Co.) 



