390 SPECIAL GEOLOGY. 



DENUDATION OP THE CHALK. This brief account of the 

 cretaceous deposits may be appropriately closed by a few re- 

 marks on the denudation of the chalk ; that is, its removal 

 from the valleys of the weald, which lie between the North 

 and South Downs. The former present a range of chalk 

 hills, which have a steep escarpment towards the south, 

 and extend from Grodahning, through Godstone, into Kent, 

 terminating in the cliffs of Dover. The latter have a cor- 

 responding escarpment towards the north, and form the 

 promontory of Beachy Head, traverse the county of Sussex 

 east and west, and pass by Hampshire into Surrey. 



At the base of these escarpments, the upper greensand 

 and the gault are found resting on the valleys of the weald. 

 The proofs of the denudation of the chalk, consist in the 

 appearance of the strata in these escarpments. They termi- 

 nate abruptly, and, it is evident, must once have extended 

 much further, since they offer precisely such appearances 

 as would be presented by the cutting of strata which were 

 previously continuous. Proofs no less conclusive are afforded 

 by the conformation of the wealden beds themselves: the 

 forest-ridge, which traverses the district in a direction nearly 

 east and west, presents a perfect anticlinal axis (fig. 267), 

 from which the strata diverge on each side towards the chalk 

 downs, affording the most convincing proof of the elevation 

 of the wealden, and the subsequent removal of the chalk" 

 and other beds, which may have been deposited upon them. 

 It is conjectured, that the tertiary strata once extended over 

 the chalk which reposed on the wealden, and covered the 

 whole area of the south-east of England. This suppo- 

 sition receives some confirmation from the outliers of the 

 tertiary beds, occurring at Castle Hill, Newhaven, and 

 near Seaford. 



In reviewing the characters of the cretaceous group, we 

 have evidence that these varied strata are the mineralised 

 bed of an extensive ocean, which abounded in the usual 

 forms of marine organic life, as algse, sponges, corals, shells, 

 Crustacea, fishes, and reptiles. These forms are all speci- 

 fically distinct from those which are discovered in the tertiary 

 strata : in many instances, the genus in all, the species 

 became extinct with the close of the cretaceous period. It 

 affords a striking illustration of creative power, that of the 



