ORGANIC MATTER IN SOILS. 53 



ash left behind on burning wood or straw, excepting 

 that there is far more of it. 



The ash from plants, it will be remembered, is but 

 a small proportion of their weight, from one to four 

 teen Ibs. in a hundred: in soils the incombustible part 

 is usually more than ninety Ibs. in a hundred, frequent 

 ly ninety-five. In some peaty or rich forest lands, 

 indeed, the organic part is largest; but, as all know, 

 these constitute but a small proportion of our ordinary 

 soils. This organic matter was not originally present 

 in the soil: it has all accumulated there by the death 

 and decay of plants and animals. The first soil, 

 formed by the crumbling and decomposition of the 

 bare rock, must have been entirely destitute of this 

 part. Some species of living things, however, existed 

 even there, some forms of vegetation and of animal 

 life ; as these died, they mingled with the broken down 

 rocks, and became food for new plants of higher or 

 ders; thus their remains gradually gathered, until the 

 result was our present surface soils. 



Fertile soils always contain a considerable propor 

 tion of this organic matter. There is no rule as to 

 the quantity that should be present: we find them very 

 fertile, containing all the way from two to fifty per 

 cent, and even upward; though it may be said that 

 permanently rich strong soils seldom contain less than 

 from five to ten per cent. 



When there is more than fifty per cent, and the soil 

 is moist, an injurious effect is produced, the soil be 

 coming what is called sour : nothing but poor wiry 

 grass will grow. The reasons of and the remedy for 

 this result, will be considered in a subsequent chapter*. 



* I have said that there is no rule as to the precise quantity of 

 organic matter that ought to be present, that is within 5 to 40 or 

 50 per cent. Other things being equal, the soil with 30 or 40 

 per cent seems to be in no way superior to that which only has 

 4 to 5 per cent. Thus we can not speak definitely as to any 

 necessary proportion. 



5* 



