ENGLISH CHALK DOWNS. 207 



luaterial. Everybody knows tluit, if in London 

 you bore deep enough tlnough the chiy wliicli 

 there forms the surface stratum of the Thames 

 basin, you come at last upon tlie i)ure and virgin- 

 wliite chalk thiit lies hidden beneath it. But in 

 many other i)laces — as, for example, along the 

 entire ridge of the North and South Downs — the 

 original capping of clay and sandstone has 

 been completely worn away, and the chalk 

 itself forms the surface of the earth, cov- 

 ered only by a shallow turf of fresh green- 

 sward, through which it is often easy to cut with 

 a knife into the underlying white deposit. The 

 fact is that, during the elevation of England which 

 produced the existing contour of the country, the 

 whole surface was not elevated equally, but was 

 pushed up into ridges along the downs and the 

 Chilterns, while it remained but little elevated 

 along the Thames valley and the Eastern Coun- 

 ties. On the higher portions, dislocated and 

 loosened as they were by the slow action of the 

 upheaving force, the rain and streams wor« away 

 gradually the overlying clays and sandstone?, till 

 they reached at last the naked chalk that lay 

 buried beneath. Nay, in certain spots — as, for * 

 example, in the Weald of Kent and Surrey — 

 where the elevating j)ower acted most forcibly, 

 the rain has even slowly worked through the 

 whole thickness of the chalk itself, and exposed 



