fcjjj ON MANURES. 



5. ifon?* C/ay, Mark, and Earth. 

 Burnt clay and In various parts of the United Kingdom it has been & 



eaith 



practice to burn clay, and clay marles, in large heaps, and 

 to spread the ashes as manure. The nature and properties 

 of burnt earth must vary with the portion of it which is 

 calcareous, as this is converted into lime by calcination. 

 Burning clay breaks its cohesion entirely, and reduces it to 

 a permanent state of friability, which does not permit it to 

 combine with any other substance: the sulphuric acid, 

 which most clays contain, is dissipated : the iron and the 

 clay itself are oxigenated : and a faculty of generating nitre 

 is given in some cases. In its burnt state also it has a power 

 of combining with the salt of urine. Burnt clays, says Dr. 

 Darwin, when strewed on the ground, may contribute to 

 vegetation, by their parting with their oxigen in a fluid, 

 not? a gaseous form ; which, uuited with carbon, or phos- 

 phorus, or nitrogen, might supply nutritious fluids to the 

 roots of vegetables. Its texture is extremely beneficial in 

 dividing and attenuating the harshness of stiff soils, and 

 rendering them more absorbent. These circumstances are 

 amply sufficient, to account for the benefit which many 

 persons have derived from the practice of burning clay and 

 marles. Mr. Leslie, in Ireland, made great exertions in 

 this way : Mr. White Parsons, in Somersetshire, has burned 

 the earth out of ditches and drains successfully : and Mr. 

 Boys, in Kent, has been long in the habit of doing it, 

 paying his men sixpence per load of ashes for digging and 



burning. 



(To be continued in our nexl.h 



X. 



