86 THE ORIGIN AND NATURE OF SOILS [chap. 



are built up. Let us now see what these products are. 

 It will first be necessary to obtain a certain number of 

 typical samples of soil ; properly they should be taken 

 with an auger or other soil-sampling tool, but for the 

 simple examination that follows they may be obtained 

 by digging a hole, 2 feet deep, with a smooth vertical 

 face, and taking off from that face uniform slices down 

 to 9 inches for the soil, and from 9 to 18 inches for 

 the subsoil. Samples should thus be obtained of both 

 soil and subsoil, from a sand, a clay, and an alluvial 

 pasture, also of the surface soil only from chalky and 

 peaty land. The samples should be spread out to dry 

 naturally on trays or sheets of paper, the lumps being 

 gently crumbled by hand before they get quite dry; 

 this being most necessary with the clay soils, which can 

 only be broken down if they are caught at just the right 

 stage of moisture. When air-dried, they must be passed 

 through a sieve having round holes, ^ inch or 3 mm. in 

 diameter, the lumps being crushed in a mortar with a 

 wooden pestle which is not hard enough to break up the 

 stones. The material passing the sieve forms the fine 

 earth required for further examination ; the stones are 

 cast away, though they should first be washed in order 

 to see of what they are composed. Now take a small 

 quantity of the fine earth of one of the soils in a little 

 dish, and heat it over a lamp, gently at first and then 

 more strongly; at the outset you will notice that it 

 begins to lose water although it was apparently dry to 

 start with, then as it becomes hotter it smokes and 

 gives off a smell of burning vegetable matter ; finally, if 

 heating is continued for some time, the soil will take a 

 bright brick-red colour and undergo no further change. 

 From this we may conclude that soils contain water and 

 a certain amount of organic matter or humus — the 

 debris of previous vegetation ; it is most instructive to 



