X 



ALTERING TEXTURE AND ABSORBENCY OP SOILS. 99 



appear, it is strictly true as to calcareous earth. In common with 

 clay, calcareous earth possesses the power of making sandy soils 

 more close and firm and in common with sand, the power of 

 making clay soils lighter, or more open and mellow. When sand 

 and clay thus alter the textures of soils, their operation is alto- 

 gether mechanical; but calcareous earth must exert chemical 

 action in producing such effects, as its power is very far greater 

 than that of either sand or clay. A very great quantity of clay 

 would be required to stiffen a sandy soil perceptibly, and still more 

 sand would be necessary to make a clay soil much lighter so that 

 the cost of such improvement would generally exceed the benefit 

 obtained. Far greater effects on the texture of soils are derived 

 from much less quantities of calcareous earth, besides obtaining 

 the more valuable operation of its other powers.* 



Every substance that is open enough for air to enter, and the 

 particles of which are not absolutely impenetrable, must absorb 

 moisture from the atmosphere. Aluminous earth, reduced to an 

 impalpable powder, has strong absorbing powers. But this is not 

 the form in which such soils can act and a close and solid clay 

 will scarcely admit the passage of air or water, and therefore can- 

 not absorb much moisture except by its surface. Through sandy 

 soils, the air passes freely ; but most of its particles are impene- 

 trable by moisture, and therefore these soils are also extremely 

 deficient in absorbent power. Calcareous earth, by rendering clay 

 more open to the entrance of air, and closing partially the too 

 open pores of sandy soils, increases the absorbent powers of both. 

 To increase that power in any soil, is to enable it to draw supplies 

 of moisture from the air, in the dryest weather, and to resist more 

 strongly the waste by evaporation of light rains. A calcareous 

 soil will so quickly absorb a hasty shower of rain as to appear to 

 have received less than adjoining land of different character ; and 

 yet if observed in summer, when under tillage, some days after a 

 rain, and when other adjacent land appears dry on the surface, the 

 part made calcareous will still show the moisture to be yet remain- 

 ing, by its darker colour. All the effects from this power of calca- 

 reous manures may be observed within a few years after their ap- 

 plication though none of them so strongly marked, as they are 

 on lands made calcareous by nature, and in which time has aided 

 and perfected the operation. These soils present great variety in 

 their proportions of sand and clay ; yet the most clayey is friable 

 enough, and the most sandy firm and close enough, to be considered 

 soils of good texture ; and they resist the extremes of both wet 



[* Professor Johnston confirms this remarkable power of calcareous 

 manures to make clay soils lighter, and light soils more close ; but (strangely 

 enough), ascribes these opposite operations to the physical or mechanical 

 action of lime. (P. 400, Agr. Chem.) 1849.] 



