210 THE MEASURE OF DURATION. 



are acted on by others present, as they would in the chemist's 

 laboratory. In the soil, there are many other matters present, and 

 some, perhaps, whose presence is not suspected ; and very complex 

 and extensive and varying combinations may exist of various mat- 

 ters, whose characters and powers are certainly not understood. 

 But while denying the correctness of his application to the soil of 

 correct and unquestioned chemical laws in regard to the known 

 matters and agencies under consideration, and while striving to 

 restrict his estimate of the extent of the operation of other agencies, 

 still I readily admit that valuable truth and good instruction are 

 to be gathered from his opinions on this branch of his subject. 

 He has enabled me to see errors in, or exceptions to the extent of 

 my own first opinion, as heretofore stated. That opinion, which 

 claimed absolute permanency for all the lime in soil (always ex- 

 cepting the minute portion taken up by plants), and Prof. 

 Johnston's opinion of the great waste and speedy removal of all 

 the lime used as manure, were both carried to very erroneous ex- 

 tremes. The true doctrine will be found between those extremes ; 

 which I trust that I have now reached, and will endeavour to 

 indicate. 



As strenuously as formerly, I still assert and maintain the per- 

 manency of lime in soil, for such amount of quantity as is at the 

 time acting chemically, or as manure. That quantity is very small, 

 compared to what is in some highly calcareous soils perhaps not 

 usually more than 1 per cent, of the whole tilled layer. Yet this 

 small quantity performs all the useful manuring functions of lime ; 

 and any excess of this earth, beyond that amount, has no manuring 

 or beneficial action. It is merely a mechanical earthy ingredient 

 which, if large, may do some good, or, as likely, some harm by its 

 presence and its mechanical bearing on the texture of the soil, but 

 is not in the least a fertilizing agent. Upon any sue-h surplus 

 quantities of either lime or carbonate of lime in soil (and perhaps 

 also some other salts of lime not required by and combined with 

 the soil, and therefore in excess), the solvent power of rain-water 

 may act, and the lime be gradually thereby removed, according to 

 the operation of chemical laws, in the manner stated by Prof. 

 Johnston. But with regard to the small quantity of lime required 

 as manure, it is (according to my original views before presented, 

 p. 96) combined chemically with the alimentary organic matter, 

 and both these, with the soil itself, and this state of combination, 

 is safe from solution or loss. The quantity of lime which may be 

 required and used as manure by a soil, varies at different times 

 according to the changes of condition. The more putrescent matter 

 the soil receives, as manure, the more lime will be required to 

 combine with, preserve, and properly utilize the organic and ali- 

 mentary matter. Any excess of lime, whether bestowed by nature, 



