GEOLOGY OF AGRICULTURE. 6T 



Let us look at a soil made ready for the Land of in- 

 dustry by those protracted agencies before described, 

 rich in all the elements of fertility, and now cleared 

 and loosened up to a reasonable depth ; and let us in- 

 quire what are the causes of its productiveness, or 

 what there is in and about that soil, which will make 

 it produce well. 



102. As we discuss this question, the learner-will 

 do well to turn back to the tables as they are referred 

 to, and refresh his memory with what has been said 

 of the substances there enumerated. Does this soil 

 contain the elements mentioned in Table I. ? The an- 

 swer is, Yes, it contains every one of them, and it 

 contains nothing else, or next to nothing ; but it does 

 not probably contain a single one of them in their ele- 

 mentary, uncombined state. 



103. We will now turn to the hinary compounds in 

 Table I. Passing by the first as unimportant and not 

 to be found in soils, we come to the second, sulphuric 

 add (SO^). Our soil will contain 1 per cent, or less of 

 this. It is found by actual analysis to form a small 

 part of all fertile soils. But in warm, sweet soils, 

 none of it is found in its acid or sour state. It is 

 combined with somer one or more of the bases (see Ta- 

 ble III.), forming a sulphate or sulphates, as with lime, 

 for instance, forming sulphate of lime (gypsum). 

 Next we come to phosphoric acid (PO*, Table I.). We 

 should expect to find from j-to ^ of 1 per cent, of 

 this, but not in its uncombined state. It exists in all 

 fertile soils, combined with lime and other bases (Ta- 



