CHAPTER XVI. 



THE RELATIONS OF GEOLOGY TO AGRICULTURE. 



XN presenting briefly the relations of geology to agriculture, as espe- 

 cially applied to New Hampshire, it seems proper first to state a 

 few fundamental facts, and then present the details that more immedi- 

 ately concern us. 



The first inquiry in agricultural geology is, What is the composition of 

 good soils .' 



The matter in all soils capable of sustaining vegetation exists in two 

 forms, — inorganic, and organic. The first contains twelve chemical ele- 

 ments, viz., oxygen, sulphur, phosphorus, carbon, silicon, and the metals 

 potassium, sodium, calcium, aluminum, magnesium, iron, and manganese. 

 In the organic part the elements are four, — oxygen, hydrogen, carbon, 

 and nitrogen. The inorganic elements are derived from the rocks ; the 

 organic elements from decaying animal and vegetable matter, — so that it 

 is of the earthy constituents we must speak. They do not indeed occur 

 in their simple state, but as water, sulphates, phosphates, carbonic acid, 

 silicates of potassa, soda, lime, magnesia, alumina, iron, etc. The aver- 

 age amount of silicates or sand in soil is eighty in one hundred parts. 



The second inquiry is, whether these elements of the soil are found 

 in the rocks. By consulting the details of their analyses, as given in 

 geological treatises, it will be seen that they are all present except phos- 

 phorus, which, however, is not unfrequently found in them in the condi- 

 tion of phosphates. Moreover, the proportion of the ingredients in the 



