218 



On the Physical Properties of Soil. 



ing water will be found better suited for countries with a greater 

 amount of rain. Those very soilsj therefore, may be fertile for one 

 country which become no longer so for another, under a change 

 of external circumstances : the usual alternation of dry and wet 

 years being, on the same principle^ more favourable to the one 

 or to the other country, according as their predominating soils 

 respectively possess a greater or a less degree of this power of 

 containing water. 



