16 CHEMISTRY, GEOLOGY 



soils naturally fertile, artificially fertilized, and 

 barren: 



The soil whose composition is found in the 

 first column of the table had yielded good crops 

 for sixty years without manure, and yet con- 

 tained an appreciable amount of all the inorganic 

 substances required by plants. The soil de- 

 scribed in the second column produced good 

 annual crops by the addition of appropriate 

 manures ; it was deficient of three or four sub- 

 stances, which were supplied by the manures. 

 The third was irrecoverably barren ; it was 

 deficient of substances wh^h none of the ordi- 

 nary manures could supply. 



Notwithstanding a soil contain* the inor- 

 ganic substances required by plants as food, it 

 may be still unproductive or barren, by the pres- 

 ence of some one largely in excess. The oxide 

 of iron, when present in a very large amount in 

 soil otherwise good, would render it incapable of 

 producing good crops. 



To remedy this evil, the land should be thor- 

 ough drained and subsoiled, so that the rains 

 might easily penetrate it and wash out the inju- 



Questions. < What will cause a soil, in other respects good, 

 to be unproductive ? How may that defect be overcome ? 



