298 



THE POPULAR SCIENCE MONTHLY. 



Other striking examples of the action of worms are found in the 

 ruins of the old Roman town of Silchester, of which Figs. 7 and 8 

 show the extent to which the basilica has been covered. In Fig. 7, 

 the concrete floor, still covered here and there with tesserae, is found 

 at three feet below the surface, and on it are piles of charred wood, 

 represented by the black. Fig. 8 does not reach to the natural sub- 

 soil. Worm-castings were observed on the floors of several of the 

 rooms, in one of which the tesselation was unusually perfect. One or 





J> 



<y 



-j 



pis 



<g^ <:^ 



Mould, 9 inches thick. 



Light -coloured earth with 

 large pieces of broken 

 tiles, 7 inches. 



Dark, fine-grained rubbish 

 with small bits oi tiles 

 20 inches. 



Concrete, 4 inches. 

 Stucco, 2 inches. 



Made bottom -with frag- 

 ments of tiles, 8 inches. 



Fine-grained made ground, 

 with the debris of older 

 buildings. 



Fig. 8. Section in the Center of tde Basilica at SiixuESTEr:. 



occasionally two open worm-burrows were found beneath all the loose 

 tesserce. Worms have also penetrated the old walls of the ruins, and 

 were found in them, with traces of the mold which they had carried 

 to them. In almost all the rooms the pavement has sunk consid- 

 erably, as Mr. Darwin shows in three sections, one of which he gives 

 (Fig. 9). Dust blown by the wind and earth washed from the hills 

 may have partly aided in covering up these buildings, but the chief 

 share of the work is attributable to worms. 



Worms also contribute to the disintegration of the rocks and the 

 denudation of the land, by generating humus acids which act on the 

 carbonate^ by grinding up in their crops the stones they swallow, and 



