AN ENGLISH SHIRE. 181 



appear higher than the clay in these places, we shall see 

 a little later. 



After the deposition of the gritty or muddy Wealden 

 beds in the lake and embouchure of the old continental 

 river, there came a second period of considerable 

 depression, during which the whole of south-eastern 

 England was once more covered by a shallow sea. This 

 sea ran, like an early northern Mediterranean, right 

 across the face of Central Europe ; and on its bottom 

 was deposited the soft ooze of globigerina shells and 

 siliceous sponge skeletons which has now hardened into 

 chalk and flint. A great cretaceous sheet thus overlay 

 the Wealden beds and the whole face of Sussex to a depth 

 of at least 600 feet ; and if it had not been afterwards 

 worn off in places, as the nursery rhyme says of old 

 Pillicock, it would be there still. I need hardly say 

 that the chalk is yet en evidence along the whole range 

 of South Downs, and forms the tall white cliffs between 

 Brighton and Beachy Head. 



Finally, during the Tertiary period, another layer of 

 London clay and other soft deposits was spread over the 

 top of the chalk, certainly on the strip between the South 

 Downs and the sea, and probably over the whole district 

 between the Channel and the Thames valley : though 

 in this case, later denudation has proceeded so far that 

 very few traces of the Tertiary formations are preserved 

 anywhere except in the greater hollows. 



Such being the original disposition of the strata which' 

 compose" Sussex, we have next to ask, What are the 

 causes which have produced its existing configuration ? 

 If the whole mass had merely been uplifted straight out 



