CLIMATIC FACTORS 



151 



On wind-swept surfaces the injurious sand-blast effect of wind goes 

 so far as to undermine and break down the sod, especially in the Elyne- 

 tum and the Caricetum firmae. Using every break in the sod as a new 

 point of attack, the wind digs and gnaws like the breakers on a rocky 



Fig. 88. — Wind erosion uncovering Populus deltoides trees that had been buried 

 in dune sand and had put out adventitious roots that are now exposed. Miller, Indiana. 

 {Photo by Fuller.) 



coast. The soil crumbs are loosened and crumbled, and roots are laid 

 bare. Lichen scales nestle in the dying tussocks, which finally break to 

 pieces and are blown away with the fine soil. The undermining and 

 destroying of the turf goes on until the nature of the soil stops it. By a 

 frontal attack, wind clefts are made (Figs. 86, 87). A lateral attack 

 results in long wind furrows, so that the outline of the ridge looks 



