Chap. VII. CONCLUSION. 311 



of a year, a horizontal line one yard in length ; 

 so that 240 cubic inches would cross a line 

 100 yards in length. This latter amount in a 

 damp state would weigh Hi 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 Mississippi, that 

 its enormous drainage-area must on an aver- 

 age be lowered '00263 of an inch each year ; 

 and this would suffice in four and 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 cannot fail to be produced within 

 a period which no geologist considers ex- 

 tremely long. 



Archaeologists ought to be grateful to 

 worms, as they protect and preserve for an 



