298 DENUDATION OF THE LAND. Chap. YI. 



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 

 l^laces, for instance on a part of Teg Down 

 near Winchester, the castings were all black 

 and did not efiervesce 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 3^ 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 which 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 



