144 STATES OF THE RIVEE PLATE. 



The mode and detail of tillage varies, however, with 

 the class of soil and the nature of the subsoil. There are, 

 as I have already stated, clayey soils —stiff clay, sUiceous 

 clay, clay loams, sandy loams, vegetable loams, peaty soil, 

 sandy soil, &c. All these varieties of soils, differing in phy- 

 sical conditions, have different powers of absorbing mois- 

 ture, heat, and food elements, and their cohesive powers 

 and tendencies are different. While in the clayey soUs the 

 most laborious tillage, the most thorough disintegration 

 and subdivision of atoms is needful, the tillage of sandy 

 soils embraces the compression of its particles, so as to 

 increase its power of retaining the moisture and food 

 elements which it absorbs ; and it is frequently found 

 requisite, when the subsoil is of a more compact nature, 

 to bring up a portion of it to incorporate with the hghter 

 surface soil, be it sandy or peaty. Sandy soils absorb 

 heat rapidly, and part with it readily. Clay soUs absorb 

 heat slowly, and retain it with tenacity ; hence, vegeta- 

 tion is parched or chilled, dwarfed or luxuriant on them 

 respectively, under different weather conditions. 



Extremes in soils are the most difficult to treat, medium 

 soils, loams of fair consistence, the easiest ; the presence of 

 organic matter effecting changes in the soil mechanically 

 and chemically in the same direction as those brought 

 about by tillage. 



On the higher and sloping lands whence the rainfall 

 rapidly drains off, a deep tillage is essential, as thereby 

 the rainfall penetrates more readily and in greater quan- 

 tity, forming a deposit or reserve of moisture which as 

 the surface dries, rises by capillary attraction as previously 

 (page 118) explained. 



On low lands a deep tillage is equally desirable, as the 

 greater the mass of soil moved, the more the land is 

 raised, and the deeper and more readily the water pene- 



