58 AGRICULTURE 



The third substance that enters into the 

 composition of all soils, and constitutes the 

 major part of many, is lime, which may be 

 present in the form of a simple carbonate, as 

 in the case of Chalk, or a double carbonate 

 of lime and magnesia, as in the case of 

 Dolomite, a type of soil which is common on 

 the Magnesian Limestone formation in the 

 north-east of England. Lime is also present 

 as a component part of certain silicates, but 

 when in this form it is not so readily avail- 

 able for the uses of plants In the Chalk 

 districts of England, where, on steep slopes 

 and escarpments, the rock comes close to 

 the surface, the soil may contain seventy per 

 cent, and upwards of carbonate of lime. 

 At the bottom of the slopes, and on the tops 

 of the hills, where the ground is more level, 

 the depth of soil is generally much greater, 

 and one may have to dig down some feet before 

 coming on chalk. Under these circumstances 

 the soil contains much less lime, in fact, on 

 the top of the Chalk Downs there may be as 

 little as one per cent, of lime in the surface 

 soil, although at the depth of only a foot or 

 two the soil may consist almost entirely of 

 this substance. Lime, in fact, is a substance 

 that is comparatively soluble in water, and 

 especially in water that is charged with 



