274 THOUGHTS IN A GEAVEL.PIT. [xi. 



the fluid sand, before the whole mass froze, as it were, 

 suddenly together. And these pebbles are nothing 

 else than rolled chalk flints. 



That settles the matter. The pebbles could not 

 come from Wales; there are no flints there. They 

 could not have been made before the chalk ; for out 

 of the chalk they came; and the only explanation which 

 is left to us, I believe, is, that over the tops of the chalk 

 downs; over our heads where we stand now, there once 

 stretched layers of sand and gravel, " Tertiary strata," 

 as I have been calling them to you ; and among them 

 layers of this same hard sandstone. 



When the floods came they must have swept away 

 all these soft sands and gravels (possibly to make the 

 Bagshot sands, of which I shall speak presently), and 

 left the chalk downs bare; but while they had strength 

 to move the finer particles, they had not generally 

 strength to move these sandstone blocks, but let them 

 drop through, and remain upon the freshly-bared floor 

 of chalk, as the only relics of a tertiary land long since 

 swept away ; while some were carried off, possibly by 

 icebergs, as far as Pirbright, and dropped, as the ice- 

 bergs melted, both there, at Dogmersfield, and also, 

 though few and small, in Eversley and the neighbour- 

 hood. 



But how came these tertiary sandstones to be so 

 very hard, while the strata around them are so soft ? 



Ladies and gentlemen, I know no more than you. 

 Experience seems to say that stone will not harden 

 into that sugary crystalline state, save under the influ- 

 ence of great heat : but I do not know how the heat 

 should have got to that layer in particular. Possibly 

 there may have been eruptions of steam, of boiling 



