Chap. III. UNDERMINED BY WORMS. 157 



of the land where worms abound toon gel 

 buried, and that large stones sink slowly 

 downwards through the same means. Every 

 step of the process could be followed, from the 

 accidental deposition of a single casting on a 

 small object lying loose on the surface, to its 

 being entangled amidst the matted roots of 

 the turf, and lastly to its being embedded in 

 the mould at various depths beneath the 

 surface. When the same field was re-ex- 

 amined after the interval of a few years, such 

 objects were found at a greater depth than 

 before. The straightness and regularity of 

 the lines formed by the embedded objects, 

 and their parallelism with the surface of the 

 land, are the most striking features of the 

 case; for this parallelism shows how equably 

 the worms must have worked; the result 

 being, however, partly the effect of the wash- 

 ing down of the fresh castings by rain. The 

 specific gravity of the objects does not affect 

 their rate of sinking, as could be seen by 

 porous cinders, burnt marl, chalk and quartz 

 pebbles, having all sunk to the same depth 

 within the same time. Considering the 

 nature of the substratum, which at Leith Hill 



