298 CAUSES OF FERTILITY AND STERILITY [chap. 



on a small scale is often seen in old gardens, 

 particularly in old town gardens which are situated 

 upon gravel soils, initially very short of the finer soil 

 particles. The constant breaking of the surface by 

 cultivation, and the use of large quantities of stable 

 manure, which decays and leaves the soil open, result 

 in a continual washing down of the finest particles, until 

 the remaining soil loses all power of cohesion and of 

 resisting drought, falling into a dusty powder immedi- 

 ately on drying. A coating of clay in the early autumn, 

 or, better still, of good marl, is the only method of 

 giving consistency to such a soil and soon remedies 

 its worst defects, such as susceptibility to drought and 

 rapid fluctuations of temperature, and tendency to 

 produce soft vegetation, very liable to disease. 



Reclamation of Peat and Heath Land. 



One of the earliest methods of bringing peat land 

 in the Fens and similar districts into cultivation was, 

 to dry the land by means of open drains and break 

 up the surface with the breast plough ; the clods were 

 then gathered together, and burnt when dry, after- 

 wards the ashes were spread and a crop of rape taken. 

 The fire was never allowed to burn too fiercely, the 

 object being to obtain charred residues rather than 

 white ashes. The effect of burning the peat was to 

 provide a certain amount of ash rich in saline matters 

 and particularly in alkaline carbonates, thus correcting 

 the two great faults of the remaining peat, its deficiency 

 in mineral matters, and its sour reaction. At the same 

 time the weeds and other coarse vegetation occupying 

 the surface were destroyed, and a clean seed-bed prepared 

 for the crop. However, the process of burning is a 

 very wasteful one, involving the loss of the combined 

 nitrogen contained in the accumulated organic matter, 



