220 ON THE CHEMICAL CONSTITUENTS OF SOILS. 



This soil is by no means remarkable for its steril- 

 ity, but is decidedly improved by manuring with 

 burned ferruginous loam. It is, however, rendered 

 still better by the use of burned marl, — a manure 

 which is rich in iron, potash, gypsum, and phosphate 

 of lime. The marl does not exert so favorable an 

 action when applied in its natural state ; but the heat 

 liberates the potash from the insoluble compound 

 which it forms with silica. 



7. Surface-soil (A) a loamy sand, from Brunswick. 

 (B) analysis of the subsoil at a depth of IJ feet. 100 

 parts contain : — 



Silica, with fine siliceous sand . 



Alumina .... 



Protoxide and peroxide of iron . 



Peroxide of manganese 



Lime, combined with silica 



Magnesia, idem 



Potash, idem 



Soda, idem .... 



Phosphate of iron 



Sulphuric acid contained in gypsum 



Chlorine .... 



Humus soluble in alkalies 



Humus, with azotized organic remains 



This soil when manured with gypsum is very fa- 

 vorable to the production of leguminous plants and 

 red clover. But it is very remarkable, on account of 

 the rust which always attacks the corn ph^nts which 

 may be grown upon it. This rust and mildew {uredo 

 linearis^ puccinia graminis) is a disease which at- 



