MECHANICAL PREPARATION OF SOILS. 45 



garden soil, and when there are trees and shrubs to be grubbed up, those 

 burned with it will impart highly fertilizing qualities. 



1 1 7. The calcining process is commenced by building up a temporary fur- 

 nace of bricks or stone, with some iron bai's laid across them for the free 

 admission of air. On this a fire is lighted, with such material as there may be 

 at hand : over that a layer of clay is placed, to which the fire soon extends. 

 ]\Iorc clay is added, and the heap extends in all directions, taking care that 

 ventilation is kept up under it, and that clay is added by degrees, mixing it 

 with fuel. In this manner the whole surface of the ground may be pared, 

 calcined, and afterwards made smooth and levelled by rolling, and the turf 

 rej^laced on places where it is to be preserved. 



118. Highly-bm'nt clay is useful as a covering for roads and paths, where 

 gravel is inaccessible ; its chief objection, as a surface material for paths, being 

 its colour ; for the oxide of iron present in all clay soils, uniting with oxj'gen, 

 gives it a dark red brick-colour. This property is usefully applied in the 

 modern style of laying out flower-beds with variegated paths ; marble and 

 granite chips being used for white and grey paths, gravel for yellow, and 

 burnt clay for red, with a very happy effect. The mode of burning clay 

 varies in different counties. Some clays burn hard when dry, others when 

 wet. In some places, where it is only required as manure, the waste coi-ners of 

 fields and scourings of the ditches are burnt in heaj)s and scattered over the 

 ground. When all the land is burned, as many as forty heaps are scattered 

 over an acre, and when reduced to about half their bulk, the fires are ex- 

 tinguished. Sometimes, however, the burning takes place in large heaps, 

 varying from two to three hundred loads, fresh materials being added as the 

 fire makes its a^jpearance outside. The object not being to burn the clay into 

 a hard red brick, however, it is just heated sufiiciently to disintegrate the 

 clay, so that it crumbles into dust between the finger and thumb. Where the 

 burning is taken by the piece, and in large heaps, the cost of digging and 

 burning is from 5d. to 7c?. the yard of ashes. When the burning is in heaps 

 forty to the acre, it costs about 85. This cost, however, increases with the 

 purity of the clay ; but the benefit derived from the process inci-eases also, 

 especially if it is not confined to simply paring and burning the surface, but 

 removing the stiff" subsoil itself, and exposing it to calcination. The secret of 

 burning strong clay is to throw it wet upon the burning heap, raking it down 

 flat as the lumps begin to crack ; thus increasing the surface exposed to the 

 action of the heat and atmosj^here ; taking care, in windy weather, to apply 

 the fresh material on the leeward side, or that side will be burnt before the 

 other is touched. Burnt in this way, the lumps will crumble under the rake 

 in a short time ; if applied dry, on the contrary, the hard lumps will become 

 harder. 



1 19. That the process of burning is highly beneficial there can be no doubt. 

 The garden of Mr. Baker, of Hardwick Court, Gloucester, consisted of a stiff 

 sterile clay : by digging out the soil three feet deep and burning it, he reu- 



