M4 



(b) Swamp ore, 5 to 8 cm. thick with 7.2S per cent, of organic sub- 

 stances : 



Soluble in Residue insoluble in 



Hydrochloric acid. Hydrochloric acid. 



Potassium 0.0178 per cent, of the soil 0.754 



(Sodium 0.0033 " " " " " 0-360) 



Calcium 0.0194 " " " " " 0.170 



Magnesia 0.0137 " " " " " 0.028 



(Manganous oxid 0.0044 " " " " " 0.047) 



Ferric oxid 0.1936 " " " " " 0.690 



Aluminum oxid 1.5266 " " " " " 2.320 



Phosphoric acid 0.2956 " 0.042 



Total mineral substances except 



silicic acid 2.0744 4.41 1 



(c) The yellowish brown sand underlying the swamp ore: 



Soluble in Residue insoluble in 



Hydrochloric acid. Hydrochloric acid. 



Potassium 0.0085 per cent, of the soil 1.103 



(Sodium 0.0213 " " " " " 0.528) 



Calcium 0.0254 " " " " " 0.225 



Magnesia 0.0401 " " " " " 0.064 



(Manganous oxid 0.0068 " " " " " 0.026) 



Ferric oxid 0.3448 " " " " " 0.760 



Aluminum oxid 0.4000 " " " " " 3-2IO 



Phosphoric acid 0.0281 " " " " " 0-043 



Total mineral substances except 



silicic acid 0.8750 5-959 



We perceive from the above figures that, by leaching, the lead sand has 

 not only lost in soluble substances, but that the greatest part of all the 

 rock debris containing nutritive substances has been decomposed by 

 weathering and being washed deeper down. It is therefore a fact that cer- 

 tain soil layers in forests and in open moors (usually formed from such soil 

 layers) become impoverished. This is very significant agriculturally if the 

 impoverishment exceeds the supply of nutriment furnished by weathering 

 and the annual rain fall. 



Meadow ore must be distinguished from the real swamp ore ; the for- 

 mer is insoluble in an acid solution, such as hydrochloric acid, while the 

 swamp ore is abundantly dissolved. 



Especially in humus moor soils, where the deposition of raw humus 

 leads to the formation of swamp ore, do two chief injurious factors come 

 under consideration : — the lack of oxygen due to the density of the soil and 

 the content in humic acids. The processes taking place, with an exclusion of 

 oxygen, have been considered in another place (for example, p. 99). 

 We have here to take only the humic acids under consideration. Graebner 

 pays the desired attention to this points Continuing Wolf's- investigations on 



1 Loc. cit. p. 228. 



2 Tagebl. Naturf, Vers., Leipzig, IS'i 



