152 GEOLOGY. 



they be wet, as any gardener may see occasionally in 

 the trodden walks. He does more than loosen the soil. 

 He brings it up in a comminuted state, as the casts will 

 show, leaving his burrows below to cave in by the 

 weight of the earth above them. Some observations 

 have been made which show that these operations are 

 of great- extent and importance. Mr. C. Darwin, who 

 made many such observations, says that " although the 

 notion may appear at first startling, it will be difficult to 

 deny the probability that every particle of earth form- 

 ing the bed from which the turf in old pasture-land 

 springs has passed through the intestines of worms." 

 If you look among the spires of grass you will find the 

 casts of these worms scattered about, for they are al- 

 ways at work swallowing earth and disgorging it, either 

 upon the surface or into their burrows. The tendency 

 of water is to wash from the surface the finer portions 

 of the soil, carrying it away or down into the ground, 

 thus leaving the coarser parts on the surface ; but the 

 earth-worms can remedy this difficulty by bringing up 

 the comminuted matter. Furnishing bait, then, for fish- 

 ing is but a small part of the earth-worm's vocation. 



The ants are also at work somewhat in the same way, 

 choosing drier spots than the earth-worms do. You 

 see them in multitudes on the dry garden walk, where 

 they make their galleries underneath, from which they 

 bring the materials for their little piles on the surface. 

 They, by loosening the soil, help to produce the vegeta- 

 tion which you are continually at work to destroy ; but, 

 though operating against you in the walk, they are every 

 where else doing a good work for you in your garden. 

 They are especially useful in tropical climates, where 

 they rapidly take to pieces, as we may say, the accumu- 

 lations of dead vegetable substance, and mingle it with 

 the soil. Dr. Livingstone, the great traveler, says of the 

 labors of the ants in the forests of Africa, "These insects 

 are the chief agents employed in forming a fertile soil. 



