On the Physical Properties of Soil. 



189 



weight previously given, we shall feel satisfied that the customary 

 terms employed by the farmer of a heavy or a light soil are 

 founded on this cohesion of the soil within itself, and adhesion to 

 agricultural implements, and therefore rather indicate its property 

 of being easier or lighter to work than its weight ; the more or 

 less easy penetration of the roots into the surrounding soil will 

 probably be in the same proportion. 



2. The consistency and firmness of soils in the dry and in 

 the wet state increase in much the same rate ; clay-lands, 

 whether in the dry or wet state, are the most difficult to work, 

 the sandy soils and those containing much humus being the 

 most easy ; when we have ascertamed the consistence of a soil in 

 its dry state, we shall be able to conclude with much probability 

 respecting its consistence in its wet state. 



3. The firmness and consistency of a soil are not in the direct 

 degree of its power of containing water ; individual earths, as fine 

 lime and magnesia, and humus, notwithstanding their great power 

 of containing water, possess but little consistency; we cannot, 

 therefore, infer the one property from the other. 



4. The consistency is generally the greatest in clayey soils ; this, 

 however, is not always the case, as the clays themselves exhibit 

 great differences according to the fineness or coarseness of their 

 grain ; fine slaty marl, notwithstanding its great proportion of 

 clay, indicates only a slight consistence ; even pipe-clay, although 

 belonging to the purest of the fine kinds of clay, has a far smaller 

 consistence than the ordinary clay of arable soils ; I found its con- 

 sistence in the dry state^ from the mean of several experiments, 

 only 42, and therefore not half so great as that of the heavy grey 

 clay of arable soils. 



5. Light soils, such as the sandy, gain much cohesive 

 power by moisture ; even the purest sand, which in its dry state 

 loses all its coherence and falls into a shapeless powder, regains 

 a certain degree of cohesiveness on being again wetted ; a damp 

 climate, therefore, with a large average quantity of rain, will be 

 found, under similar circumstances^ more advantageous to sandy 

 districts. 



6. In the case of all the earths, the adhesion to a surface of 

 wood is seen to be 8:reater than to one of iron, a circumstance occa- 

 sioned, without doubt, by wood, even in its finished state, pre- 

 senting more points of contact than iron to the damp earth ; this 

 might appear to be contradicted, by land in wet weather being 

 often more capable of being worked with wooden than with iron 

 implements, such for instance as harrows ; the reason of this, how- 

 ever, is to be sought, not in the smaller adhesion of the soil to the 

 wood, but frequently in the circumstance of iron implements, from 

 their greater weight, sinking deepej into the soil in wet weather 

 than wooden ones. 



