Actum of the Atmosphere upon neioly-deepened Soil. 441 



G40 lbs. to every acre in the year. {Johnstons Elements of 

 Agricnlt. Chemistry., 5th etl., p. 216.) Can it be thought that 

 this ingredient is alone snatched up from the sea-waters and all 

 the rest left behind ? To suppose so would be absurd, and altliough 

 the others may exist in the rain in proportions so small as to 

 have escaped notice, like the ammonia and nitric acid, yet there 

 can be little doubt that the total amount thus carried down to 

 the soil in a season must have an aj-jpreciable influence on vege- 

 tation. The annual average fall of rain in Britain on the plains 

 amounts to about 554,000 gallons per imperial acre, and on the 

 mountain ranges to nearly double this : although therefore the 

 amount of any of these salts in a gallon may be quite inap- 

 preciable, yet when multiplied 554,000 times the product may 

 give a very important quantity. 



Rain-water on reaching the ground begins to dissolve a part 

 of almost everything it meets with in its passage through the 

 soil, such as carbonates and phosphates of lime, magnesia, and 

 iron, silicates of lime, potash, and soda, organic matters, &c. 

 By looking into the mineral matters found in springs and rivers, 

 which are merely rain-water that has percolated through or over 

 the soil, some idea will be got of its solvent powers. Tiie 

 following table shows the various substances found in some well- 

 known rivers : — 



The following tahh' coiitaiii.s the analyses of two springs in the 

 Malvern hills of South AX'alcs, from the Memoirs of the Geological 

 Surrci/, ^()l. ii. p. 17. The rocks of these hills are composed, 

 according to Mr. Phillips, principally of the minerals, quartz, 



