ANIMAL AGENCY IN BOIL-MAKING. 485 



about its mouth. The result is the overturning of a considerable 

 amount of the earth, and a consequent commingling of the material 

 with vegetable matter. When brought to the surface and left exposed 

 to the action of frost, the breaking up of the material is greatly favored, 

 and thus the formation of the soil is facilitated. 



Considerable as is the effect of burrowing mammals, the principal 

 overturning of the earth in our primeval forests is accomplished by the 

 invertebrate animals. Where the woods are not very dense, and par- 

 ticularly where the soil is somewhat sandy, our largest species of ants 

 are very effective agents in working over the soil. Their burrows ex- 

 tend to the depth of some feet below the surface, and each hill brings 

 to the air several cubic feet of excavated matter, which, as slight in- 

 spection shows, is much commingled with vegetable matter. Wher- 

 ever these ant-hills abound they commonly exist to the number of a 

 score or more on each acre, and the occupants of each hill, in many 

 cases, bring as much as a cubic foot of matter to the surface in the 

 course of a single year. The action of rain constantly operates to 

 diffuse this material on every side of the hill. We may often observe 

 a thin layer of sediment extending for a considerable distance from 

 the elevation. 



As is well known to all those who have inspected the soil within 

 virgin forests, the earth is occupied by a host of larval insects, princi- 

 pally belonging to the group of beetles, but including also many 

 orthopterous insects. These creatures, in the course of their life un- 

 derground, displace a good deal of soil, a portion of which is thrown 

 upon the surface, the greater part, however, being merely dislodged be- 

 neath the surface. The effect, however, is to commingle and to break 

 up the soil, and thus favor its comminution. Although the roots of 

 trees do by far the larger part of the rending which is accomplished in 

 the soil-layer, they do not bring about much commingling of the soil. 

 The thrusts which they apply to it shear the materials about, and so, 

 to a certain extent, mix them, but by far the larger part of the com- 

 mingling is effected by the animal life which dwells beneath the 

 forest-bed. 



Where the woods are wet and favor the development of the cray- 

 fish, the effect of this group of animals on the overturning of the soil 

 is extremely great. It probably exceeds that which is accomplished 

 in our ordinary fields by the action of the earth-worms. A single 

 cray-fish will often bring in the course of a single season's activity not 

 less than half a cubic foot of earthy matter to the surface. In certain 

 districts where these animals abound, there appear to be not less than a 

 thousand to each acre of surface. If such be their number, it is evi- 

 dent that not less than five hundred cubic feet of matter is brought to 

 the surface from a considerable depth in the course of a year. As this 

 matter is generally of a rather fine nature and easily dissolved in 

 water, it rapidly washes away and forms a thin sheet on the surface. 



