COMPOSITION OF LOCAL SPRINGS. 21 



local rocks. The waters of such streams, springs, and runlets 

 are never pure. They are always impregnated with saline or 

 mineral matter to some extent ; and the nature as well as the 

 quantity of this mineral matter depends upon the chemical 

 composition of the rocks which the water has traversed or run 

 over. 



Waters issuing from limestone regions are loaded with car- 

 bonate of lime. When they come from red sandstone districts, 

 or from the deep Oxford clay, common salt and gypsum often 

 abound. Springs arising among the coal measures are sometimes 

 rich in carbonate of soda ; from dolomitic rocks and from mica 

 slates, in salts of magnesia ; and, from granites and decaying 

 felspars, in salts of potash and soda.* 



Such waters passing through, or over, or under the surface 

 of a soil, cannot fail to affect its productiveness in a sensible 

 degree. What the soil is deficient in, they may supply. What 

 we add as a trial manure, they may already bring in the 

 required proportion to the growing plant ; and thus the results 

 of actual experiment may be in opposition to the apparent natu- 

 ral wants of the soil, as indicated by analysis, or to results 

 obtained with the same substance in other localities placed, to 

 all appearance, in precisely similar circumstances. Local and 

 limited springs may produce local and circumscribed effects. 

 In ignorance of the existence and composition of such springs, 

 it would be impossible to calculate upon their presence, or to 

 make an allowance for their effects upon the crops. 



* The surface water of ponds in the county of Huntingdon contains as much 

 as 40 grains of mineral matter to the imperial gallon. In wells in the same 

 county sunk into the Oxford clay, it amounts (at Melshburne, Lord St John's) to 

 upwards of 70 grains in the gallon. It consists chiefly of carbonate and sulphate 

 of lime. The water of the Thames contains about 14, and that with which 

 Edinburgh is supplied about 10 grains in the gallon. 



