332 WAVES OF SAND AND SNOW 



among the aeolian sand-waves called fuljes, 

 which I described in a previous chapter (see 

 Plate LXXL). 



Sarid-reefs in the Mississippi. 



The engineers of the Mississippi River Com- 

 mission have made many observations upon the 

 ridge-and-furrow formation of the sandy bottom 

 of the Mississippi near Bullerton and Eulton, where 

 the waters of Mississippi and Ohio are not com- 

 pletely blended, although the distance below their 

 junction is about loo miles. These ridges or reefs 

 are not exactly at right angles to the current, 

 neither do they progress without change of form. 

 They are, therefore, hardly to be considered as 

 truly waves. 



" The wave (as the sand-reef is termed by the 

 engineers) retains its position until some change 

 in velocity disturbs or displaces the eddy, when 

 its rapid destruction, either partial or total, follows, 

 after which a new wave is formed under the new 

 conditions . . . motion rarely takes place except 

 during the obliteration of the wave, when a part 

 of the material scoured from it is deposited imme- 

 diately below, thus flattening the front slope and 

 carrying the crest down-stream. After the wave 

 has under this action entirely lost its original 



