ON THE USE OF LIME, MARL, AND SHELL-SAND. 



21 



It is a curious fact that sometimes farmers find it answer 

 their purpose to sink deep pits in localities that are situated on 

 the chalk formation, and to apply the lower chalk to the surface- 

 soil, already containing abundance of chalk. Irrational as this 

 may appear at first sight, this practice finds a ready explanation 

 and defence in modern chemical researches, for these tell us that 

 the lower chalk beds often contain so large a proportion of 

 phosphate of lime that even bones or superphosphate, when used 

 as manures on soils formed by the direct disintegration of lower 

 chalk beds, are without efficacy ; whilst on land formed by the 

 decomposition of the upper chalk beds, bones or superphosphate, 

 or even the chalk from lower beds, produce the same striking 

 effect, especially on root-crops, which usually attends the use of 

 phosphatic manures. 



There are soils in Somersetshire, I am informed, in the neigh- 

 bourhood of Ilminster, where superphosphate of lime is of no use 

 whatever; and as here the lower chalk formation prevails, it 

 would be very interesting to ascertain whether those soils on 

 which superphosphate shows no effect contain more than a suffi- 

 cient quantity of phosphoric acid to answer all the purposes for 

 which superphosphate is employed in agriculture. It must not 

 be supposed, however, that all beds in the chalk formation be- 

 come richer the deeper they are situated, nor that the beds which 

 are described by geologists as belonging to the lower chalk are 

 necessarily richer in phosphoric acid than those nearer the 

 surface or the upper chalk beds. This will appear clearly from 

 the subjoined Table, in which are arranged the results of analyses 

 of several varieties of chalk, from different beds of the chalk 

 formation. These analyses, made by Professor Way, at the same 

 time may serve to illustrate the composition of different varieties 

 of chalk : 



Analysis of Chalks. 



