262 The Origin and Mode of Formation of the Vaile of Wardour. 
flank of that uprising some day a coal-field may be discovered ! 
But again the land was to be covered by the sea. No doubt that 
long dome-like ridge had, during the time it was above water, been 
carved by rain action, and to some extent wasted, but the waves 
once more covered it, as it sank beneath the shallow Pliocene Sea, 
which planed across the flexures of the anticlinal, and produced what 
is called a “plain of marine denudation,” a result which, when a 
country is sinking, and its hills are gradually eaten away, the waves 
of the sea produce. 
This marine action here swept away the whole of the Chalk from 
the centre of the vale, exposing the Upper Green Sand, and possibly 
the Gault, with the Kimeridge Clay outside them to the west. 
After the erosive planing action of the Pliocene Sea, an easterly 
dip was given to the whole country, causing all the beds to slope 
gently towards the east, so that there was a great undulating plain 
formed, with an eastward inclination. 
On this newly-emerged country fresh influences immediately began 
to work—rain to fall, and frost to break up the rocks. 
In what direction would the streamlets begin to flow? They 
would, from the very first, run down the eastward sloping plain ; 
they would choose the direction that offered least resistance. 
It may appear strange to us, when we look at the valley now, 
with its wide mouth open to the west, and a double range of hills 
bounding it north, south, and east, that the drainage did not escape 
westward, where there are no hills, or hard rocks, but only a low 
expanse of Kimeridge Clay, rather than flow, as it does, in the 
other direction, out of the narrow end of the vale, and breach a range 
of hills 500ft. high. 
But, we must recollect that then no hills barred the way, for there 
was no valley as yet, only an open undulating plain, sloping gently 
to the east, consisting of Clay on the west, and of the Gault, Green 
Sand, and Chalk over the site of the present valley of the Nadder. 
As a rule, in the same direction as streamlets begin to run, so 
they continue when they become brooks and rivers—their initial 
direction is carried on. When a line of drainage is once graven on 
the surface of the country hardly anything can alter it. The line 
i 
