98 THE SOIL. 



the composition of the well-water at Briickenau to the 

 solvent action of rain percolating through a humose soil, 

 rich in decaying vegetable substances. (' Annal. der Chem. 

 und Pharm.' i. c. 285.) 



It is clear that wherever conditions have been at work 

 similar to those under which the bog-water in the Botanic 

 Garden of Munich and the wells of Briickenau have been 

 formed, the water found on the sm-face of the earth, in 

 pools, springs, or brooks, will contain in the most varying 

 proportions nutritive elements useful to plants, such as 

 phosphoric acid and potash, which are not found in other 

 waters. Li like manner, an arable soil rich in vegetable 

 remains, in which, from the processes of decay incessantly 

 going on, products of an acid character are generated, 

 will be able to give up, to the rain-water percolating 

 through it, phosphoric acid and alkalies, which are thus 

 carried down to the deeper layers, and appear in the 

 drainage water. The quantity of these substances dis- 

 solved in the water will depend upon the condition of the 

 soil on which the plants grow, the ash constituents of which 

 are carried away by the rain-water, from their decaying 

 remains. Where the ground is rocky, covered with a 

 thin coating of earth and a thick clothing of fohage, the 

 water which runs off will carry down to the lower layers 

 all the more fixed elements of vegetable food, in propor- 

 tion as the layer of earth itself retains less of them. The 

 finer earthy particles of such a soil, washed away by 

 heavy rains, are carried down by torrents to the valleys 

 and low lands, and form a soil of all degrees of fertihty 

 according to their chemical condition, which determines 

 their power of absorbing dissolved nutritive substances. 

 But these layers of earth formed from the mud borne 

 down by the torrents will always either be saturated, or 

 gradually become saturated with the nutritive substances 



