4 6 SOILS. 



consequence of imperfect drainage. Such a condition, always 

 injurious to plants, becomes doubly so when it is associated 

 with the formation of a metallic solution, such as ferrous 

 carbonate, and promptly results in the languishing or death of 

 plants in consequence of the poisoning of their roots. In the 

 presence of sulfates such as gypsum, the formation of iron 

 pyrites (ferric bisulfid) and sulfuretted hydrogen, is likely to 

 take place. Moreover, under the same conditions the phos- 

 phoric acid of the soil may be concentrated into ferrous or 

 ferric phosphate, which pass into deposits of bog ore in the 

 subsoil. 



