484 THE POPULAR SCIENCE MONTHLY. 



AXIMAL AGENCY IX SOIL-MAKING. 



Br Peofessoe N. S. SHALEK. 



THE admirable studies of Mr. Darwin on the influence of earth- 

 worms upon the soil has made it clear that these animals exercise 

 a most important effect in its preparation for the use of plants. Mr. 

 Darwin's luminous essay has served to call attention to the effect of 

 organic life on the development of the soil-coating. In the following 

 pages I propose to submit the results of some studies of a general 

 nature, which serve to show that a number of other animals have a 

 considerable influence on the i:)reparation of soils. 



Our soils, as is well known, depend upon a variety of actions 

 which serve to break up the rocky matter of the earth, and to commin- 

 gle that matter with organic materials more rapidly than the erosive 

 agents can remove the detritus from the point at or near which it 

 decays. For the formation of the soil two actions, at least, are essen- 

 tial. First, the bed-rock must be broken into fragments sufiiciently 

 separated from each other to permit the passage of roots between 

 them ; second, the rock fragments must be still further comminuted 

 and commingled with organic waste to make the combination of or- 

 ganic and inorganic matter on which the utility of the soil absolutely 

 depends. Although the earth-worms are undoubtedly very important 

 agents in overturning and breaking up of soil, it appears to me that 

 they are most effective in the tilled fields or in the natural and artificial 

 grass-lands. So far as I have been able to observe, these creatures are 

 rarely found in our ordinary forests where a thick layer of leaf-niold, 

 commingled with branches, lies upon the earth. The chai'acter of this 

 deposit is such that the creatures are not competent to make their 

 way through it, and they therefore in the main avoid such situations. 

 Moreover, wherever the soil is of a very sandy nature, earth-worms 

 are scantily found if they are present at all. These worms are practi- 

 cally limited to the soils of a somewhat clayey character, which have 

 no coating of decayed vegetation upon them. 



As the greater portion of the existing soil has been produced in 

 forest regions, I shall first examine the action of various animals upon 

 the soils of wooded countries. The mammals are, of all our vertebrates, 

 the most effective in their action upon the soil of forests. Twenty 

 species or more of our American mammals are burrowers in the forest- 

 bed. They either make their habitations beneath the ground, or resort 

 to it in the pursuit of food. Of these, our burrowing rodents are per- 

 haps the most effective, but a large number of other small mammals 

 resort to the earth and make considerable excavations. In forming their 

 burrows, or in the pursuit of other burrowing animals, these creatures 

 often penetrate through the whole or greater portion of the soil-cover- 

 ing. The material which is withdrawn from the burrow is accumulated 



