CuAi>. VI. MOULD OVER THE CHALK. 297 



whole it appears tliat the crowns and fur- 

 rows on land formerly plou^^hed, but now 

 covered with grass, fend slovrly to disappear 

 when the surface is inclined ; and this is pro- 

 bably in large part due to the action of 

 worms ; but that the crowns and furrows last 

 for a very long time when the surftice is 

 nearly level. 



Formation and amount of mould over the 

 Chalk Formation. — Worm-castings are often 

 ejected in extraordinary numbers on steep, 

 grass-covered slopes, where the Chalk comes 

 close to the surface, as my son William 

 observed near Winchester and elsewhere. If 

 such castings are largely washed away during 

 heavj^ rains, it is difficult to understand at 

 first how any mould can still remain on our 

 Downs, as there does not appear any evident 

 means for supplying the loss. There is, more- 

 over, another cause of loss, namely in the per- 

 colation of the finer particles of earth into the 

 fissures in the chalk and into the chalk itself. 

 These considerations led me to doubt for a time 

 whether I had not exaggerated the amount 

 of fine earth which flows or rolls down grass- 

 covered slopes under the form of castings ; and 



