THE BRAIN OF THE EARTH 



soils may contain an excess of injurious acid 

 material. In each case the soil requires a 

 different treatment. The chemists and soil ex- 

 perts, in turn, tell the farmer what changes are 

 advisable, or, in case the soil has never been 

 cultivated, indicate to the prospective settler 

 just what crop the soil is best suited for. 



The difference between soils and the impor- 

 tance of understanding this difference was 

 brought closely to the writer's attention in 

 preparing a series of microscopic photographs 

 to illustrate rich and lean soils. 



Taking a pinch of earth from one of the 

 richest wheat lands on the globe, it was placed 

 on a slide under the microscope. A knock 

 from the finger and the thickest portion was 

 removed, leaving only a faint dust upon the 

 slide. But, faint as this dust was, it was yet 

 too dense for photography, so it was necessary 

 to blow hard upon the glass in order to re- 

 move every loose particle and leave only an 

 almost imperceptible film. And yet, so mar- 

 velously rich was this soil in vegetable-mold, 

 so near together the billions of particles in a 

 gram, it was only by the utmost care that a 

 photograph could even then be made. 



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