TO STUDY THE COMPOSITION OF SOILS 5 



that have resulted from the breaking and grinding of 

 large rocks, to which has been added some organic material 

 which has been formed by the decay of plant and animal 

 remains. All of the light-colored rock particles in the 

 bottles are quite similar except as to size. The dark 

 material at the surface or floating in the water is organic 

 matter which may be removed from the soil by burning. 

 Both classes of material are essential to the growth of 

 plants, the rock particles furnishing the mineral food 

 elements and the organic matter the nitrogen. The organic 

 matter also increases the moisture-holding capacity of the 

 soil. 



