Formation of Soil. 



Darwin, through a long and careful study, reached the 

 conclusion that in many parts of England earthv/orms pass 

 more than 10 tons of dry earth per acre through their 

 bodies annually and that the grains of sand and bits of flint 

 in these earths are partly worn to fine silt by the muscu- 

 lar action of the gizzards of these animals. Their method 

 of action in moving through the soil is this: They eat a 

 narrow hole, swallowing the earth, when the point of the 

 head is held fast in the excavation while an enlarged por- 

 tion of the oesophagus or swallow is drawn forward, forc- 

 ing the cheeks outward in all directions, thus crowding the 

 soil aside and making the opening wider, when more dirt 

 is eaten and the operation repeated, allowing the animal 

 to advance through the soil. 



Domestic fowls ..and all seed-eating birds, in picking up 

 pebbles for service in grinding their food, do the same sort 

 of work as the earth- 

 worms in producing 

 fine soil, as every 

 housewife can testify 

 from the worn condi- 

 tion of bits of glass 

 and pottery taken from 

 the gizzard of the 

 chicken. 



77. Soil Convection. 

 There is another very 

 important line of work 

 done by earthworms. 



/ ' 



ants and all burrowing 

 animals, in bringing 

 the sub-soil to the sur- 

 face and carrying the 

 surface soil into the 

 ground, thus maintain- 

 ing a sort of soil-con- 



,. , . , . f FIG. 22. A to wer-liko casting. ejected by a spe- 



VectlOn Which, in ei- cies of earthworm, from the Botanic Garden, 



f . , , ,1 Calcutta, India. Natural size from photo, 



tect, amounts tO tne (After Darwin.) 



