190 BUEIAL OP THE EBMAINS Chap. IV. 



beneath the floor and walls, which it is prob- 

 able were formerly as numerous as they now 

 are, had not collapsed in the course of time 

 in the manner formerly explained, the under- 

 lying earth would have been riddled with pas- 

 sages like a sponge ; and as this was not 

 the case, we may feel sure that they have 

 collapsed. The inevitable result of such col- 

 lapsing during successive centuries, will have 

 been the slow subsidence of the floor and of the 

 walls, and their burial beneath the accumu- 

 lated worm-castings. The subsidence of a 

 floor, whilst it still remains nearly horizontal, 

 may at first appear improbable ; but the case 

 presents no more real difficulty than that of 

 loose objects strewed on the surface of a field, 

 which, as we have seen, become buried several 

 inches beneath the surface in the course of a 

 few years, though still forming a horizontal 

 layer parallel to the surface. The burial of 

 the paved and level path on my lawn, which 

 took place under my own observation, is an 

 analogous case. Even those parts of the 

 concrete floor which the worms could not 

 penetrate would almost certainly have been 

 undermined, and would have sunk, like the great 



