EXPERIMENTS WITH CRUSHED LIMESTONE. 227 



of lime. These differences throw much light on the cause of 

 the preference which, in every district, practical men are found 

 to give to one lime over another for this or that kind of soil. 

 A knowledge of these chemical differences not only suggests 

 experiments with the view of testing such opinions of practical 

 men, or of putting to the proof the deductions to which the 

 analyses point, but it teaches us also what to look for among 

 the effects they produce, and to make our experiments with a 

 definite end. 



3. Suggestions for experiments with crushed limestone. 



Marls, limestone gravels, corals, and shell sands, are all known 

 to be useful applications to the soil, and to be very economical 

 where they plentifully occur. Crushed limestone ought to act in 

 a similar way, and to be similarly useful. As, therefore, the full 

 fertility of the land in our climate is not to be brought out 

 without the use of lime in some form, I would suggest that 

 trials should be made with limestones artificially crushed, where 

 circumstances render the burning of them either difficult or 

 unprofitable. 



There are two cases in which the crushing of limestone may 

 be recommended ; 



1. Where the expense of fuel is so great as to render it im- 

 possible to burn lime profitably. 



2. Where the limestones are of so impure a quality, or so 

 full of earthy and siliceous matter, as to refuse to slake after 

 they are burned. In this case they are at present considered 

 unfit for agricultural purposes, though many of them, when 

 burned and crushed, are employed as cements. But if crushed 

 by mechanical means, a limestone that is fit for no other pur- 

 pose may be applied with advantage to the land. Such lime- 

 stones occur in many districts which at present are supposed to 

 possess no available agricultural lime. The adoption of this 

 method of crushing in those districts might place within the 

 reach of practical men a means of agricultural improvement of 

 which they have hitherto been unable to avail themselves. 



Two circumstances ought generally to conspire in order that 



