164 MARLING PREVENTS WASHING EFFECTS OF RAINS. 



field that has been injured "by washing, many of the old gulleys 

 will begin to produce vegetation, and show that a soil is gradually 

 forming from the dead vegetables brought there by winds and 

 rahis, although no means had been used to aid this operation. 



[This newly acquired ability to resist the washing power of rains, 

 is one of the most beneficial effects of marling on hilly lands. 

 And this effect is no less certain, than it is conformable to the 

 theory of the action of marl and to reason. On soils containing 

 very little lime (or almost none, as in naked sub-soils), whether 

 they be sandy or clayey, there is nothing to combine the vegetable 

 matter with the soil, nor the different ingredients of the soil with 

 each other. Consequently they have no cohesion, and whenever 

 made very soft, or semi-fluid by rains, and there is any declivity, 

 there is nothing to prevent the soil, or upper surface, being washed 

 off by excessive rain, though falling gently. Of course, torrents 

 of rain produce the same injurious effects much more rapidly and 

 effectually. But when such soils have been made calcareous, a 

 chemical combination and bond of union and coherence is formed 

 between the lime and the putrescent or organic matter, and of both 

 with the silicious and argillaceous parts of the soil ; which combi- 

 nation is able to resist any but an unusual force of the washing 

 action of rains.* Moreover, by the increase of productive power 

 thus given, grass grows more kindly and rapidly, and by its decay 

 the vegetable mould is continually augmented, and thereby the 

 power of resisting washing is still more increased as the fertility 

 of the soil is increased. This is but another aspect and operation 

 of the power of calcareous manure in soils to fix and retain 

 manures. 



The tendency of some very sandy soils to be moved, and in part 

 blown away, by high winds, is also produced by the want of cohe- 

 sion of the particles. The wind operates on the soil in its dry 

 state in the same way, and for the same defect of its constitution, 

 as does water in rain torrents. The same remedy, calcareous ma- 

 nure, is even more effectual to prevent the wasting operations of 

 wind than of water. The absorbent power given to the before 

 loose and more rapidly drying particles of sandy soils serves to 

 preserve more moisture at the surface. This alone would tend 

 much to prevent the moving effect of the wind, which can take 

 place only on earth nearly or quite dry and pulverulent. Further, 

 both directly and indirectly (by combining the . organic with the 

 earthy parts), the calcareous manure, when thoroughly diffused, 

 interposes some cohesive particles between the particles of sand. 



* Confirmation. Johnston speaks of organic (or putrescent) matter be- 

 ing presented to the action of lime " in the state of chemical combination 

 with earthy substances with the alumina, for example, and with lime and 

 magnesia already existing in the soil." p. 402. 



