302 
MR. PRESTWICH ON THE GEOLOGY OE THE DEPOSITS 
have existed between the two countries ; but as the raised beaches of later date prove 
an elevation of the land subsequent to the period of the high-level gravels, the old 
channel must have been larger in the proportion of the ditference of level so produced 
to the difference which would have resulted from the wear of the land alone. That 
the elevation of the Wealden area had taken place before this period is proved by the 
occurrence of high-level gravels within its limits (see Map, Plate IV.), whilst the hydro- 
graphical conditions of the whole area show that those deposits hold the same relative 
position to the adjacent coast in one part as in another ; whence I should infer both 
a widening of the sea-channel, and a former somewhat greater extent of land. 
With reference to the condition of things at the time of the low-level gravels the 
evidence is more positive. We have old cliffs running nearly parallel with the present 
line of coast, and estuarine deposits in position nearly coincident with the like 
modern deposits. There are the old cliffs and raised beach at Brighton on the one side 
of the channel, and those at Sangatte, near Calais, on the other, while the deposits 
near Havre, Abbeville, and on the Stour, near Canterbury, furnish us with examples of 
estuarine beds of this late postpliocene age. On a coast so exposed to the action of the 
sea, and with cliffs constantly though slowly yielding to its incessant action, it is not to be 
expected that traces of old raised beaches should be preserved, except at a few sheltered 
spots. These we have at places so closely allied to the present contour of coast — 
showing, too, old cliffs forming, like the present range of cliffs, bold escarpments to an 
old sea — that although I conceive the channel to have been considerably widened since 
then, I am satisfied that it existed at the time of the low-level gravels, whatever doubt 
there maybe of its prior existence. There is no palaeontological objection to this view, 
inasmuch as the land and freshwater Mollusca had spread over this country at an anterior 
period; the greater bulk of them had in fact made their appearance in this country 
previous to the Boulder Clay, and many at the period of the Crag. A nearly similar 
observation applies, with few exceptions, to the Mammalia. With a climate, however, 
such as we have inferred, and with a channel of less breadth than the present one, the 
sea between the two lands might have been frozen every winter and have allowed of the 
passage of man and large animals, as happens at this day in latitude 52° at the island 
of Saghaleen, where the strait between it and the adjacent mainland is frozen every 
winter for a period of some months*. 
Nor are we entirely without evidence, although very slight, derived from the land 
Mollusca, of the existence at this latter period of a barrier impassable to them. There 
are two species, the Pomatias obscurus and Clausilia pliccttula , Drap., living French 
shells, both of which I have found fossil at Menchecourt, but which are not known 
either living or fossil in England. 
All these phenomena indicate long periods of time. I do not, however, feel that we 
are yet in a position to measure that time, or even to make an approximate estimate 
* On the east coast of Saghaleen the sea freezes every winter as far as the eye can reach. Occasionally the 
Tiger crosses over to that island. — Ravenstbin’s ‘ Amur,’ pp. 284 & 320. 
