Ch. XXI.] CHALK ESCARPMENTS 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 outf. This steep declivity is called 
by geologists 6 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, 
You III. U 
