190 



THE SOIL: INORGANIC MATTER 



4. Peat Soils. — These are composed for the most part of 

 organic matter but little decomposed (Fig. 43). The tissue 

 of the plants of which they are composed is still plainly dis- 

 tinguishable. Unless these soils are in a limestone region 

 decomposition results in the production of a considerable 

 degree of acidity. The mineral matter present frequently 

 amounts to no more than 10 or 15 per cent. 



Fig. 43. — Peat soil. Soils Department, Wisconsin Station. 



5. Muck Soils. — These are soils containing large amounts 

 of organic matter, but which are in a more advanced state 

 of decomposition than peats. Plant tissue is quite indis- 

 tinguishable and there is very much more mineral matter 

 present. 



6. General Composition. — Table XI gives the approximate 

 composition of sand, clay, muck, and peat soils in three 

 principal constituents, nitrogen, phosphoric acid, and potash. 

 The figures, while not applicable in every case, will at least 

 give an idea of relative differences as they very commonly 

 occur. The weight of the surface eight inches of sand is 

 taken at 2,500,000 pounds, of clay at 2,000,000, of muck 

 at 1,000,000, and of peat at 350,000. 



Table XI. — Composition or General Soil Types. 



