On Paring and Burning. 351 



Tlie more rlav a soil contains, the more retentive and the stifFer 

 it is; the more impervious the subsoil upon which it rests, the 

 less perfectly air ran find access to the interior of the soil and 

 the more rapidlv these vegetable remains increase in it. Hence 

 the laro:e proportion of organic matter which is found in land 

 resting on the impervious forest marble clay, a description of 

 clay which I believe would not be unproductive if it were 

 efficiently drained, and altered in its physical characters by other 

 approved mechanical means. Hence also the large amount of 

 vegetable remains in land laid down in permanent pasture, or 

 in soils after one or two years' growth of clover or sainfoin. 



In clover-lea or old sainfoin soils there is a great abundance 

 of vegetable matter, arising from the clover roots and decayed 

 leaves, as well as from the weeds, couch, thistles, &c., grown 

 upon it. Generally vegetable matter in sufficient quantity can 

 be raked together to burn a larire quantity of soil, without the 

 addition of any other combustible matter. On burning, the 

 organic portion of these vegetable remains is. destroyed for the 

 greater part, and the mineral and saline matters contained in 

 every kind of vegetable matter are left behind, mixed with clay 

 and other mineral matters of the soil, more or less changed by 

 the action of the fire. 



The general character of the ashes left on burning vegetable 

 matters, freed as much as possible from adhering eartli, may be 

 illustrated by two analyses, made some time ago in my laboratory. 



1 selected for examination two weeds, which infest very gene- 

 rally the calcareous clay soils and brashy land on the Cotswold 

 hills, namely, the stemless thistle (Carduus acaulis) and couch. 

 The first when gathered contained from 25 to 26 per cent, of dry 

 substance and 74 to 75 per cent, of water, and left on burning 

 9"66 j)er cent, of ash. 



Tl)e ash of this thistle submitted to a partial analysis furnished 

 in 100 parts : — 



Composition of the Ash of the Stemless Thistle (Carduus acaulis'). 



Potash and chloride of pot.issium .. .. 27'40 



Chloride of sodium "UO 



Lime 41-44 



Mao:nesia 4-40 



(Xxide of iron and alumina 2'01 



Phosphoric acid 5'36 



Sulphuric acid 2*92 



Sohible siHca and sand 3'50 



Carbonic acid, and loss 12'07 



100-00 



Lime it will be seen is the principal constituent of this ash. 

 This may account for the fact that this thistle delights to grow 



