270 THOUGHTS IN A GRAVEL-PIT. [xi. 



the chalk farrowed, worn into deep pits, which are 

 often filled with sand, and gravel, and rounded lumps 

 of chalk. You may see this for yourselves, in the 

 topmost layer of any chalk -pit round here. You may 

 see, even, in some places, the holes which boring shells, 

 such as work now close to the tide-level, have made in 

 it ; all the signs, in fact, of the chalk having been a 

 rocky sea-beach for ages. 



The first bed which you will generally find upon the 

 water-worn surface of the chalk is a layer of green- 

 sand and green-coated flints. Among these are met 

 with in many places beds of a great oyster, now un- 

 known in life. I cannot say whether there are any 

 here; but at Reading, to the east of Farnham, at 

 Croydon, and under London, they are abundant. 

 There must have been miles and miles of oyster-bed at 

 the bottom of that Eocene sea ; among the oyster-beds, 

 beds of a peculiar pebble, which we shall see in our 

 gravel-pit. 



They are flints ; but very small, dark, often almost 

 black, and quite round and polished. Compare them 

 with the average flints of the pit, and you see that 

 while the average flints are fresh from the chalk, these 

 have plainly been rolled and rounded for years. They 

 are (except in their dark colour) exactly such shingle 

 as forms the south-coast beach about Hastings and 

 Brighton. They are the shingle beaches of the Eocene 

 sea, part of which are preserved under the London clay. 

 To the north a vast bed of them remains in its original 

 place, on Blackheath near London ; while part, in the 

 district to the south, which the London clay has not 

 covered, have been washed away, and carried into our 



