132 RELATIONS OF SOIL TO WATER 



preponderating influence in determining the agricultural value 

 of land, considerable improvements in the character of the 

 soil may often be effected by artificial means, if we bear in 

 mind the facts laid down in the preceding pages. As the 

 same causes, and the same modes of cure, apply as a rule 

 both to cases of deficiency and excess of water supply, and 

 to cases of deficiency and excess in the tenacity of the soil, 

 we shall most conveniently consider these subjects together. 



In a coarse sand we have a soil of minimum tenacity, and 

 also one of minimum capacity for retaining water. The 

 evils due to lack of tenacity are exemplified in the case of 

 blowing sands. When these sands are in a bare dry condition, 

 the wind separates the finer and more valuable particles, 

 and then rolls over the coarser grains, which may thus be 

 carried in great drifts to considerable distances, rendering 

 much land infertile. If such land can be permanently covered 

 with vegetation, the mischief we have described will be of 

 course prevented. Where a coarse sand is found naturally 

 covered by a pine forest, it will be a great mistake to cut 

 down the forest and attempt arable culture. The establish- 

 ment of perennial plants having widely spread roots is a first 

 step in the reclamation of blowing sands. Shelter from wind 

 must also be provided. Fences will check the progress of 

 sand in the same way as the groins on the seashore hinder 

 the movement of the shingle. 



King has investigated the question of the agricultural treat- 

 ment of the blowing sands of Wisconsin (Wisconsin nth 

 Rep., 292). He points out the great diminution in the velocity 

 of the wind which results even from shelters of small height 

 above the ground. Land left ploughed in ridges across the 

 prevailing direction of the wind was little injured when a 



