II.] TYPICAL SOILS 55 



finer particles and of humus ; good wheat land or 

 land that will form sound permanent pasture will 

 contain at least 30 per cent, of silt and clay. The 

 ease with which a soil suffers the rain to percolate 

 depends upon the relatively low proportion of silt and 

 clay rather than on the amount of coarse-grained 

 material; the fine particles pack in among the larger, 

 and the soil is equally resistent to the passage of water, 

 whether the finest material is diffused among coarse 

 sand and gravel, or among the finer grades of sand. 

 The shrinkage of a soil on drying, and its tenacity when 

 dry, are even more dependent on low proportions of 

 coarse sand, humus, and chalk, than on the actual 

 amount of clay and silt which cause the shrinkage. 

 The really difficult soils to work are those containing 

 less than 20 per cent, of sand above 01 mm. in 

 diameter. 



The table on page 56 will serve to illustrate these 

 points. 



Soil No. I represents one of the lightest of sands, 

 about the extreme limit of cultivation — a soil, indeed, 

 which had been found unfit for ordinary farming, 

 and had been planted with conifers. 



It will be seen that more than 83 per cent consists 

 of " sand," nearly all of the coarser kinds, while the clay 

 only amounted to 4-7 per cent, most of which was really 

 ferric oxide. Calcium carbonate is also entirely absent, 

 owing to which the soil accumulates more humus than 

 would be expected from its great aeration, and in the 

 hollows where water lies it often becomes peaty. Such 

 soils are rarely in cultivation, but are left as wastes, 

 carrying a natural vegetation of heather and pine. 



Because, however, of their lightness and warmth, 

 they are sometimes valuable for market gardening on a 

 small scale, if they are so situated that large supplies of 



