Chap. II. EXCAVATION OF THEIR BURROWS. 101 



depth, and was of so poor a nature that 

 weeds could not grow on it. It is therefore 

 highly improbable that it should have been 

 swallowed by the worms as food. Again in 

 a field near my house the castings frequently 

 consist of almost pure chalk, which lies at only 

 a little depth beneath the surfoce ; and here 

 again it is very improbable that the chalk 

 should have been swallowed for the sake of 

 the very little organic matter which could 

 have percolated into it from the poor over- 

 lying pasture. Lastly, a casting thrown up 

 through the concrete and decayed mortar 

 between the tiles, with which the now ruined 

 aisle of Beanlieu Abbey had formerly been 

 paved, was washed, so that the coarser 

 matter alone was left. This consisted of 

 grains of quartz, micaceous slate, other rocks, 

 and bricks or tiles, many of them from -^-^ to 

 ■jL inch in diameter. No one will sujipose 

 that these grains were swallowed as food, yet 

 they formed more than half of the casting, 

 for they weighed 19 grains, the whole cast- 

 ing having weighed 33 grains. Whenever a 

 worm burrows to a depth of some feet in 

 undisturbed compact ground, it must form its 



