Chap. III. BKOUGHT UP BY WORMS. 141 



been left on the surface and forms a bed of 

 stiff red clay, full of flints, and generally 

 from 6 to 14 feet in thickness. Over the red 

 clay, wherever the land has long remained as 

 pasture, there is a layer a few inches in 

 thickness, of dark -coloured vegetable mould. 



A quantity of broken chalk was spread, 

 on December 20, 1842, over a part of a field 

 near my house, which had existed as pasture 

 certainly for 30, probably for twice or thrice 

 as many years. The chalk was laid on ' the 

 land for the sake of observing at some future 

 period to what depth it would become buried. 

 At the end of November, 1871, that is after an 

 interval of 29 years, a trench was dug across 

 this part of the field ; and a line of white nodules 

 could be traced on both sides of the trench, at 

 a depth of 7 inches from the surface. The 

 mould, therefore, (excluding the turf) had 



on the same principle that a trunk of a tree left on a glacier 

 assumes a position parallel to the line of motion. The flints 

 in the clay which form almost half its bulk, are very often 

 broken, though not rolled or abraded ; and this may be ac- 

 counted for by their mutual pressure, whilst the whole mass is 

 subsiding. I may add that the chalk here appears to have been 

 originally covered in parts by a thin bed of fine sand with some 

 perfectly rounded flint pebbles, probably of Tertiary age ; for such 

 sand often partly fills up the deeper pits or cavities in the chalk. 



