42 DARWINISM STATED BY DARWIN HIMSELF. 



weigh eleyen and a half pounds. Thus a considerable 

 weight of earth is continually moving down each side of 

 every valley, and will in time reach its bed. Finally, this 

 earth will be transported by the streams flowing in the 

 valleys into the ocean, the great receptacle for all matter 

 denuded from the land. It is known from the amount 

 of sediment annually delivered into the sea by the Missis- 

 sippi, that its enormous drainage-area must on an average 

 be lowered "00263 of an inch each year ; and this would 

 sufiBce in four and a half million years to lower the whole 

 drainage-area to the level of the sea-shore. So that, if a 

 small fraction of the layer of fine earth, -2 of an inch in 

 thickness, which is annually brought to the surface by 

 worms, is carried away, a great result can not fail to be 

 produced within a period which no geologist considers 

 extremely long. 



THEY PEESEETE TALITABLE EUINS. 



Archaeologists ought to be grateful to 

 ° " worms, as they protect and preserve for an 

 indefinitely long period every object, not liable to decay, 

 which is dropped on the surface of the land, by burying 

 it beneath their 'castings. Thus, also, many elegant and 

 curious tesselated pavements and other ancient remains 

 have been preserved ; though no doubt the worms have 

 in these cases been largely aided by earth washed and 

 blown from the adjoining land, especially when culti- 

 vated. The old tesselated pavements have, however, 

 often suffered by having subsided unequally from being 

 unequally undermined by the worms. Even old massive 

 walls may be undermined and subside ; and no building 

 is in this respect safe, unless the foundations lie six or 

 seven feet beneath the surface, at a depth at which worms 



