SLEBJENTS OF AGRICULTURE 
I! 
PART SECOND. 
CHAPTER I. 
LESSON I. 
GENERAL isOixtox DERATIONS OF THE SOIL, AND THE CAUSES 
THAT AFFECT ITS VALUE. 
1. That portion of the earth turned up by the plough, 
and in which plants are developed, is called the soil. 
2. That portion of the earth which is not cultivated, and 
which lies immediately beneath the soil, is called the sub¬ 
soil. In certain cases, it is advantageous to bring a por¬ 
tion of the sub-soil to the surface, which is effected by 
deeper ploughing or digging than usual; the depth of the 
soil is increased, and by this means better crops are ob¬ 
tained. We will see presently, however, that there are 
circumstances in which the soil would not be at all bene¬ 
fited by this course. 
3. The soil is formed of two kinds of principles: some 
are of vegetable and animal origin, the others are of mine¬ 
ral origin. These last form the earth properly so called, 
and constitute the activity of the soil; the first its richness. 
4. That a soil may yield abundant crops, it is necessary 
that its activity should be in proportion to its richness; 
but it is generally the first quality that predominates, in 
which case the yield is but little. 
5. From what precedes, we must see that almost all 
soils must differ in value; for it is rare to find two pre- 
siseiy alike as regards composition. In some (and it is 
