222 THE DARWINIAN THEORY 



over a field, had sunk an inch in about five years, or 

 one-fifth of an inch per year. In the case of a stony 

 field with very scanty vegetation, and covered 

 thickly with flints, some half the size of a child's 

 head — all these had disappeared in thirty years. 



The weight of the castings, collected and dried, 

 which were ejected on a square yard of ground on 

 Leith Hill Common during a year, amounted to over 

 7 lbs., or 1 6 tons per acre. 



At Stonehenge some of the outer ring of stones 

 have fallen, and are now partially buried in the soil, 

 owing to the action of worms. The specific gravity 

 of objects does not affect their rate of sinking. In 

 fact, "worms have played a more important part in 

 the history of the world than most persons would at 

 first suppose." 



Hensen placed two worms in a vessel eighteen 

 inches in diameter, which was filled with sand on 

 which fallen leaves were strewed : these were soon 

 dragged into burrows to a depth of three inches. 

 After about six weeks an almost uniform layer . of 

 sand, nearly half an inch thick, Was converted into 

 mould, from having passed through the alimentary 

 canals of these two worms. 



It is not difficult to account for the success which 

 this work achieved. " In the eyes of most men the 

 earthworm is a mere blind, dumb, senseless, and 

 unpleasantly slimy annelid. Mr. Darwin undertakes 

 to rehabilitate his character, and the earthworm 

 steps forth at once as an intelligent and beneficent 

 personage, a worker of vast geological changes, a 

 planer down of mountain-sides, a friend of man." 



