8 THE SOIL OF THE FARM. 



may not show the greatest depth of weathered band upon 

 the surface, owing to the removal of the particles as soon 

 as disintegrated. 



Denudation. — The same weather action which forms 

 soil is also wasting or carrying them away. Soil is al- 

 ways travelling towards the sea. It is deepest in the val- 

 ley and thinnest on the brow of the hill. The land 

 movement consists for the most part of the mere sweep- 

 ing downwards of its component particles by ram or 

 thawing snow, or by surface drainage. The continued 

 rainfall not only dissolves out of the soil a great deal of 

 the soluble matter, but must eventually remove much of 

 the soil itself. Indeed, our brooks and rivers, after 

 heavy long-continued rain, show us by the yellow muddy 

 color of their waters that they are carrying a vast quan- 

 tity of sediment to the sea. All this sediment has come 

 from the most easily washed oft parts of the surface soil, 

 upon which the rains have persistently been falling. It 

 is, however, the fact that the soil, notwithstanding, re- 

 mains nearly constant in quantity. Though, therefore, 

 it is continually washed away, it is augmented from other 

 causes, just as much on an average as it is diminished by 

 denudation; and this augmentation evidently can pro- 

 ceed from nothing but the constant and slow disintegra- 

 tion of the underlying rock. If there were not a con- 

 comitant decomposition of the subsoils, converting them 

 into surface soils, the solid rock would everywhere appear 

 naked at the surface, as is the case in mountainous dis- 

 tricts where the wasting away of the soil is more rapid 

 than the rate of decomposition of the underlying rocks. 

 Even the tillage and plowing of arable lands plays into 

 the hands of the robbing weather action, by enabling it to 

 act more powerfully on the soil, and to waste it in a 

 liigher degree than it could have done liad it l)ecn ])rotect- 

 ed by natural vegetation or by the grass of pasture laud. 



