246 ENGLISH CHANNEL IN PART A VALLEY OF DENUDATION. 
the strata of Dover and the hills west of Calais # , and by Mr. De 
la Beche, between the strata of the coast of Dorset and Devon, and 
those of Normandy-p, it may be inferred (after making due allowance 
for the possible influence of those earlier causes, which in many in¬ 
stances have occasioned valleys) that the English Channel is a sub¬ 
marine valley, which owes its origin in a great measure to diluvial 
excavation, the opposite sides having as much correspondence as 
those of ordinary valleys on the land. According to Bouache, the 
depth of the Straits of Dover is on an average less than 180 feet; 
and from thence westward to the chops of the Channel the water 
gradually deepens to only 420 feet, a depth less than that of the 
majority of inland valleys which terminate in the Bay of Charmouth; 
and as valleys usually increase in depth from the sides towards their 
centre, so also the submarine valley of the Channel is deepest in the 
middle, and becomes more shallow towards either shore. 
It seems probable, that a large portion of the matter dislodged 
from the valleys of which we have been speaking, by the diluvian 
waters to which they owe their origin, has been drifted into the princi¬ 
pal valley of this district, viz. the bed of the sea; and being subse¬ 
quently carried eastward, by the superior force of the flowing above 
that of the ebbing tide, and the prevailing storms from the south¬ 
west, has formed that vast bed of pebbles known by the name of the 
Chesil Bank: the principal ingredients of which are.such as on the 
above hypothesis they might be expected to be; viz. rolled chalk- 
flints, and pebbles of chert j;; the softer parts of the materials that 
# See Geol. Trans, vol. v. pp. 47, &c. -f Ibid. vol. i. of New Series, p. 89- 
J This hypothesis has received a further confirmation from the discovery, by the 
Hon. Wra. Strangways in the summer of 1828, of the molar tooth of an elephant, among 
