SOILS AXD MANURES. 351 



loosens the compact soil. It is thought that earth-worms 

 are more beneficial than injurious, because the benefit which 

 they confer by loosening the soil is greater than the dam- 

 age which they do by extracting nutriment from it. 



488. "Water in the Soil. Food for either plant or animal 

 needs to be dissolved to be available, and the great solvent 

 is water. If a drought prevail plants languish, not because 

 there is a deficiency of nourishment in the soil, but because 

 there is not sufficient water to present the nutritious mat- 

 ter in good quantity to the absorbents, and to carry it up 

 in the tubes of the plants. You saw in 484 that a large 

 amount of water is required for this. The solid matter of 

 nutrition must be carried along on a full tide in the chan- 

 nels made for it. 



489. Soil as Generally Constituted. Soil is commonly 

 made up of many substances mingled together, but derived 

 from two sources. The first is the rocks. The great bulk 

 of the soil conies from this source. This is very manifest 

 in gravelly and sandy soils, for in them a mere glance 

 shows you the broken pieces and grains which carrie from 

 the rocks. But it is true even of fine rich earth that the 

 most of it is mineral, and therefore that the rocks furnished 

 it. You can see this to be so if you take some earth in 

 your hand and examine it after it is dry. You will find 

 that the grains of stone predominate over the other ma- 

 terials. An analysis of the earth will develop the fact 

 more thoroughly, for two reasons. First, some of the in- 

 gredients from the rocks are dissolved in the water of the 

 earth ; and, secondly, some of them are very finely divided, 

 and therefore their mineral character is not manifest to the 

 naked eye. The second source of soil is the decay of veg- 

 etable and animal matters. All wood, leaves, bones, flesh, 

 etc., as they decay form a part of the soil. 



490. Humus. This second part of the soil is called hu- 



