Ch. XXL] CHALK ESCATIPMENTS ONCE SEA-CLIFFS. 289 



In attempting to account for the manner in which the five 

 secondary groups above mentioned may have been brought into 

 their present position, the following hypothesis has been very 

 generally adopted. Suppose the five formations to lie in 

 horizontal stratification at the bottom of the sea ; then let a 

 movement from below press them upwards into the form of a 

 flattened dome, and let the crown of this dome be afterwards 

 cut off, so that the incision should penetrate to the lowest of 

 the five groups. The different beds would then be exposed on 

 the surface in the manner exhibited in the map, plate 5 *. 



It will appear from former parts of this work, that the amount 

 of elevation here supposed to have taken place is not greater 

 than we can prove to have occurred in other regions within 

 geological periods of no great duration. On the other hand, 

 the quantity of denudation or removal by water of vast masses 

 which are assumed to have once reached continuously from the 

 North to the South Downs is so enormous, that the reader may 

 at first be startled by the boldness of the hypothesis. But he 

 will find the difficulty to vanish when once sufficient time is 

 allowed for the gradual and successive rise of the strata, during 

 which the waves and currents of the ocean might slowly accom- 

 plish an operation, which no sudden diluvial rush of waters 

 could possibly have effected. 



Escarpments of the chalk once sea-cliffs. In order to make 

 the reader acquainted with the physical structure of the Valley 

 of the Weald, we shall suppose him first to travel southwards 

 from the London basin. On leaving the tertiary strata he will 

 first ascend a gently-inclined plane, composed of the upper 

 flinty portion of the chalk, and then find himself on the summit 

 of a declivity consisting, for the most part, of different members 

 of the chalk formation, below which the upper green-sand, and 

 sometimes also the gault crop out^. This steep declivity is called 

 by geologists ( the escarpment of the chalk,' which overhangs a 



* See illustrations of this theory by Dr. Fitton, Geol. Sketch of Hastings. 

 f We use this term, borrowed from our miners, to express the coming up to the 

 surface of one stratum from beneath another* 

 VOL, III. U 



