298 DENUDATION OF THE LAND. Chap. "VI. 



I sought for additional information. In some 

 places, the castings on Chalk Downs consist 

 largely of calcareous matter, and here the 

 supply is of course unlimited. But in other 

 places, for instance on a part of Teg Down 

 near Winchester, the castings were all black 

 and did not efi'ervesce with acids. The mould 

 over the chalk was here only from 3 to 4 

 inches in thickness. So again on the plain 

 near Stonehenge, the mould, apparently free 

 from calcareous matter, averaged rather less 

 than 3J inches in thickness. Why worms 

 should penetrate and bring up chalk in some 

 places and not in others I do not know. 



In many districts where the land is nearly 

 level, a bed several feet in thickness of red 

 clay full of unworn flints overlies the Upper 

 Chalk. This overlying matter, the surface 

 of whicb has been converted into mould, con 

 sists of the undissolved residue from the chalk. 

 It may be well here to recall the case of the 

 fragments of chalk buried beneath worm- 

 castings on one of my fields, the angles of 

 which were so completely rounded in the 

 course of 29 years that the fragments now 

 resembled water-worn pebbles. This must 



