140 AMOUNT OP EABTH Chap. III. 



here been thrown up at an average rate of 

 •22 inches per year. Beneath the line of 

 chalk nodules there was in parts hardly any 

 fine earth free of flints, while in other parts 

 there was a layer, 2J inches in thickness. In 

 this latter case the mould was altogether 9i 

 inches thick ; and in one such spot a nodule 

 of chalk and a smooth flint pebble, both of 

 which must have been left at some former 

 time on the surface, were found at this 

 depth. At from 11 to 12 inches beneath 

 the surface, the undisturbed reddish clay, full 

 of flints, extended. The appearance of the 

 above nodules of chalk surprised me much 

 at first, as they closely resembled water- 

 worn pebbles, whereas the freshly-broken 

 fragments had been angular. But on ex- 

 amining the nodules with a lens, they no 

 longer appeared water-worn, for their surfaces 

 were pitted through unequal corrosion, and 

 minute, sharp points, formed of broken fossil 

 shells, projected from them. It was evident 

 that the corners of the original fragments of 

 chalk had been wholly dissolved, from pre- 

 senting a large surface to the carbonic acid 

 dissolved in the rain-water and to that gener- 



