103 



EARTHS AND SOILS. 



are ever furnished by nature, are entirely barren, nor 

 would any addition of putrescent manures enable 

 either of the earths to support healthy vegetable life. 

 The mixture of the three earths, in due proportion, 

 will correct the defects of all ; and, with a sufficiency 

 of animal or vegetable matter, a soil is formed. Such 

 is the natural surface of almost all the habitable world ; 

 and though the qualities and value of soils are as vari- 

 ous as the proportion of their ingredients, yet they are 

 mostly so constituted, that no one earthy ingredient is 

 so abundant but that the texture of the soil is mechan- 

 ically suited to the production of some valuable crop. 

 Some plants require a degree of closeness, and others 

 of openness, in the soil, which would cause other plants 

 to decline or perish. As the qualities and value of 

 soils depend on the proportions of their ingredients, 

 and the grand desideratum in agriculture is to obtain a 

 mixture of the earths best calculated to produce the 

 greatest variety of the most valuable crops, we can 

 satisfactorily comprehend in what manner that object 

 may be obtained. Silicious and aluminous earths, by 

 their mixture, serve to cure the defects of each other. 

 The open, loose, thirsty and hot nature of sand being 

 corrected by and correcting in, turn the close, adhesive, 

 and wet qualities of aluminous earth. This curative 

 operation, however, is merely mechanical, and it seems 

 probable that calcareous earth, when in large propor- 

 tion, also aids the corrective power of other earths. In 

 addition, also, to the mechanical effects of calcareous 

 earth, it possesses chemical powers more effectual in 

 altering the texture of soils, and for which a com- 

 paratively small quantity is sufficient. The chemical 

 action of calcareous earth, as an ingredient of soils, 

 will be particularly noticed hereafter, when we come 

 to the consideration of the food of plants. From what 

 has been said, it would appear reasonable to class and 

 name soils according to their predominant earthy in- 

 gredients which exert the greatest power, and most 



