Chap. VI. ANCIENT MOUNDS. 291 



beneath which many worm-castings were 

 found. These had flowed bodily downwards, 

 and others had rolled down as pellets. Hence 

 it is certain that as long as a mound of this 

 kind is tenanted by worms, its height will be 

 continually lowered. The fine earth which 

 flows or rolls down the sides of such a mound 

 accumulates at its base in the form of a- talus, 

 A bed, even a very thin bed, of fine earth is 

 eminently favourable for worms ; so that a 

 greater number of castings would tend to be 

 ejected on a talus thus formed than elsewhere : 

 and these would be partially washed away by 

 every heavy shower and be spread over the 

 adjoining level ground. The final result 

 would be the lowering of the whole mound, 

 whilst the inclination of the sides would not 

 be greatly lessened. The same result would 

 assuredly follow with ancient embankments 

 and tumuli ; except where they had been 

 formed of gravel or of nearly pure sand, as such 

 matter is unfavourable for worms. Many old 

 fortifications and tumuli are believed to be at 

 least 2000 years old ; and we should bear in 

 mind that in many places about one inch of 

 mould is brought to the surface in 5 years or 



