IX.] 



CHALKING 



3" 



In place of lime, chalk may often be used with 

 advantage when it is readily accessible ; for example, on 

 one side of the Chalk formation the Gault and the upper 

 beds of the Lower Greensand, and on the other side the 

 London Clay and the Bagshot Sands, are generally in 

 need of lime, and are never very remote from the out- 

 crop of the chalk. The superficial clays and sands 

 lying on the Chalk itself are often deficient in lime, and 

 may be readily chalked by sinking shallow pits. It 

 must be remembered that much larger quantities ot 

 chalk than of lime are needed to produce a given effect ; 

 not only is the chalk equivalent chemically to about 

 half its weight of lime, but in practice it can never be 

 reduced to so fine a state of division as lime obtains by 

 careful slaking. In chalking, it is desirable to obtain 

 the soft upper white chalk from a pit, so that it is 

 saturated with quarry water ; if then spread over the land 

 in autumn it gets frozen while still full of water, and 

 becomes reduced to a comparatively fine powder which 

 can be ploughed in if on arable soil or spread with 

 a harrow on the pastures. Very large quantities of 

 chalk are used, up to 100 loads to the acre; naturally 

 the effect of such treatment is more permanent than 

 the usual liming. 



