228 EXPERIMENTS WITH DIFFERENT 



this mechanical crushing may be economically adopted. The 

 limestone to be crushed, and water-power to set the crushers in 

 motion, ought to be near each other, that the cost of transport 

 may be avoided. In many hilly and mountainous districts this 

 is the case, and in such localities the method is worthy of a 

 trial. 



4. Suggestions for comparative experiments with different 

 chalks and marls. 



1. Chalks. It is a matter of extensive local observation, 

 that the upper and under beds of chalk possess different agri- 

 cultural virtues.* So much is this the case, that farmers will 

 bring the latter from a great distance, while the former abounds 

 on their own farms. The reason of this has never been satis- 

 factorily explained. I do not find it anywhere distinctly stated 

 either what are the differences in the qualities and composition 

 of the chalks, or in the sensible effects which they severally pro- 

 duce. Do they differ in the quantities of earthy matter, or in 

 the proportions of phosphate of lime, or of other fertilising ingre- 

 dients they respectively contain ? Are their effects mechanically 

 different only ? Does the one consolidate or open the soil more 

 than the other, and are they, on this account, preferred respec- 

 tively according as the soil is light or heavy ? Does the one fall 

 under the winter's frost more readily than the other, and does 

 it thus mix more thoroughly with the soil ? 



I would suggest that some careful observer should apply to 

 the same land, in equal quantities, the two kinds of chalk that 

 the different effects should be specially noted from year to year 

 that their effects on unlike soils should be personally ob- 

 served, or where different kinds of cropping are followed and 

 that a rigorous analysis of the kinds of chalk employed should 

 be obtained at the same time. By this course of procedure, 

 some light would be thrown upon what is at present incapable 

 of a rational explanation. 



2. Marls differ in value, in the estimation of practical men, 

 no less than chalks and limestones. I would here, however, 



* See Use of Lime in Agriculture, p. 28 ; and JOHNSTON'S Elements of Agri- 

 cultural Chemistry, 4th .edition, p. 85. 





