242 RELATIONS OF GEOLOGY TO THE SUCCESS 



of the ear ; if they influence in different ways the quality of 

 the turnip crop, or of grass for feeding, and so on. 



Observations of this kind, suggested by what we know of the 

 composition of different varieties of lime, will not only test our 

 theoretical views, and give us clearer ideas as to the special 

 effects of the substances which different limestones contain upon 

 our different crops, but will also lead practical men in each 

 district to the employment of that variety of lime which, under 

 all the circumstances, is likely to yield them the largest return 

 of pecuniary profit. 



3. Connexion of the geology of a district with the probable 

 success of experiments with lime in general, or with lime of 

 different varieties. 



There are certain geological considerations which the experi- 

 menter upon the use of lime may usefully bear in mind, both 

 in reference to the localities in which the application of lime 

 generally is recommended, and to those in which limes rich in 

 magnesia or other substances may be tried with comparative 

 safety, and with the hope of advantage. Thus 



1. Where the average proportion of lime in the rocks of the 

 country is small, it may be assumed as almost certain in our 

 climate that the application of lime is likely to be followed by 

 profitable improvement. On the other hand, where the rocks 

 are rich in lime there is a presumption that the soils, or the 

 springs that water it, will also contain it in considerable quantity. 

 In regard to this point, however, no safe conclusion can be 

 drawn from purely geological considerations. There are so 

 many circumstances which conspire to remove lime from the 

 soil, that a chemical analysis, or a careful testing with acid, can 

 alone be depended upon in proof of its containing a sufficient 

 natural supply of this necessary ingredient. 



2. In districts which abound naturally in magnesia, the use 

 of purer limes such as the chalks and mountain limestones is 

 indicated. Where the rocks are poor in magnesia, though the 

 strongly magnesian limes may not be proper for ordinary and 

 general use, yet an admixture of them with other limes, or an 



