A RAMBLE THROUGH CATERHAM VALLEY. 137 



with these strata is that, speaking generally, they 

 form a hollow basin, in which lie London and its 

 suburbs, their extremes cropping out in precisely 

 the same order in a northerly direction from London 

 as we have stated they do towards the south. The 

 London Clay which fills the basin stretches from 

 Croydon to St. Albans ; the chalk from Box Hill 

 to Dunstable ; the Greensand from Dorking to 

 Leighton Buzzard ; and the Lower Greensand from 

 Reigate to Ampthill. The Oolites of the north 

 thin off as they approach London, and, though they 

 are met with in the Metropolitan borings, yet they 

 do not appear in the southern region as do the 

 Cretaceous deposits. 



Next in geological age to the Greensand, forming 

 part of the Cretaceous series, is the Wealden Clay. 

 This bed, along with the underlying Hastings Sand, 

 constitutes the bottom of the Cretaceous formations. 

 The Wealden Clay resembles the London Clay in 

 this, that it, also, lies in a basin, the northern and 

 southern boundaries of which agree in respect to 

 the order in which the various beds crop out. A 

 traveller coming from Chichester northwards to 

 Horsham would meet with the same kinds of deposits 

 and in the same order as would a traveller going 

 from London southwards towards Horsham. The 

 beds both would cross are the Lower Eocene (London 

 Clay, etc.), Chalk, Upper Greensand, Gault, Lower 

 Greensand, and Wealden Clay. The advantage 

 which the Londoner would have over the traveller 

 from the south is that he would find the various 

 strata squeezed together more closely in his track, 



