315 
The third instance was that of a stiff clay, from 
Mount’s Bay, Cornwall. This land had been 
brought into cultivation from a heath by burning 
about ten years before ; but having been neglected, 
furze was springing up in different parts of it, which 
gave rise to the second paring and burning. 100 
parts oflhe ashes contained 
8 parts of charcoal. 
2 of saline matter, principally common salt, 
with a little vegetable alkali. 
7 Oxide of iron. 
2 Carbonate of lime. 
Remainder alumina and silica. 
Here the quantity of charcoal was greater than 
in the other instances. The salt, I suspect, was 
owing to the vicinity of the sea, it being but two 
miles off. In this land there was certainly an ex- 
cess of dead vegetable fibre, as well as unprofitable 
living vegetable matter ; and I have since heard, 
that a great improvement took place. 
Many obscure causes have been referred to for 
the purpose of explaining the effects of paring and 
burning ; but I believe they may be referred en- 
tirely to the diminution of the coherence and tena- 
city of clays, and to the destruction of inert, and 
useless vegetable matter, and its conversion into 
a manure. 
Dr. Darwin, in his Phytologia, has supposed, 
that clay during torrefaction may absorb some nu- 
tritive principles from the atmosphere that after- 
wards may be supplied to plants ; but the earths 
are pure metallic oxides, saturated with oxygene ; 
