HOW SOILS ARE MADE AND MIXED 9 



goes to build up the animal's body. The rest is thrown 

 off and becomes a part of the soil. Sooner or later the 

 animal dies, and its body, too, goes back to the earth 

 again. Thus we see that soil becomes the meeting place 

 of the mineral kingdom and the kingdom of life. 



Animals not only help to make soils, but they also play a 

 very important part in mixing them through and through. 

 Gophers spoil our alfalfa, clover and timothy fields, and 

 we try to keep them out. The same is true of ground 

 hogs, squirrels and other digging animals; and yet these 

 rodents have for ages performed an important part in soil 

 making. Each ant-hill is a real soil-mixing mill. 



Perhaps the most important visible member of animal 

 life in soil making and mixing is the common earthworm, 

 angleworm, or fishworm, as we may choose to call it. 

 " These insignificant creatures burrow in moist, rich soil 

 and derive their nourishment from the organic matter it 

 may contain. In order, however, to obtain this com- 

 paratively small amount of nutritive matter, they devour 

 the earth without any selective power and pass it through 

 their alimentary tracts, rejecting the non-nutritious 

 portions, which nearly equal in bulk that first taken in. 

 The numerous holes made, while in part perhaps to afford 

 passage to the surface, are mainly excavated in this 

 process of soil eating, and actually represent the amount 

 of material which the worms have passed through their 

 digestive systems. 



" Darwin states that in certain parts of England these 

 worms bring to the surface every year, in the form of 

 excreta, more than ten tons per acre of fine, dry mold, ' so 

 that the whole superficial bed of vegetable mold passes 

 through their bodies in the course of every few years.' 

 By collecting and weighing the excretions deposited on a 

 small area during a given time, he found that the rate of 



