62 REASONS OF BARRENNESS. 



bring it up by ploughing in green crops, and thus 

 gradually with a moderate use of manure in addition, 

 form a surface soil. This would, however, be a work 

 calling for the exercise of much patience, perseverance, 

 and good judgment. 



The foregoing table shows clearly enough, the 

 differences in soils which cause what we call fertility 

 or barrenness. The explanation is perfectly simple, 

 and perfectly satisfactory, showing as it does that all 

 depends upon the presence or absence of certain sub 

 stances. This is the general solution, but there are 

 occasionally cases which form exceptions. There are 

 soils which remain barren, even although they contain 

 all of the substances named above, and though much 

 manure is added. This is because their physical 

 structure and condition is wrong, or because some 

 substances are present in hurtful excess, a. If the 

 quantities of magnesia, iron, or manganese, be very 

 great, the soil containing them is f6und to be un- 

 propitious to vegetation, often positively injurious. 

 b. There are two oxides of iron occasionally found 

 in the earth. One is the peroxide, or common iron 

 rust; this does not seem to be hurtful, but always 

 beneficial to vegetation. The other is called the 

 protoxide of iron; it contains less oxygen than the 

 peroxide, it is also more soluble, and is where it 

 exists in considerable quantity, fatal to most plants 

 and trees. 



A barren soil, then, is barren because some sub 

 stances are too largely present, or because certain sub 

 stances are wanting. Chemistry is quite competent 

 to point out the difficulty in either case, and also to 

 say what would be the remedy. We can tell what is 

 necessary to fertilize the most hopeless desert, but at 

 the same time may not be able to conduct the opera 

 tion so as to make it profitable. It becomes no longer 

 a question of knowledge, it is one of expense. We 



