222 Geology of the Straits of Dover. (April, 
English side, the Wimereux and the Slack on the French 
side. Perhaps at that time, or at a still earlier period, the 
South Downs also stretched across the Channel, to join the 
chalk escarpment on the south of Boulogne. Between the 
North and South Downs there would be a mass of high 
land, ranging nearly east and west, jeining the high cliffs of 
Fairlight with those of La Créche. 
The North Downs are now cut through by several rivers 
which drain the Weald; they are from east to west,—the 
Stour, the Medway, the Darent, the Mole, and the Wey. 
Whatever causes may have formed their valleys will also 
have formed the old valley in the Straits of Dover, which 
we may call that of the Rother. But there is no evidence 
to prove that any one of these valleys owes its formation to 
disruption of the strata; they have all been wholly excavated 
through the solid rocks by the rivers which run in them. 
We have, therefore, no reason to suppose that the Straits 
of Dover has been caused by faults or dislocations. On the 
contrary, we have every reason to suppose that the beds 
range uninterruptedly across from shore to shore. 
There is probably no geological formation in England 
through which more tunnels or deep cuttings have been 
made than through the Chalk. All the railways, in ap- 
proaching London, from the north, west, or south, must pass 
the Chalk escarpment; and although advantage has usually 
been taken of valleys which break through the escarpment, 
yet in many cases tunnels have been necessary. These 
tunnels and deep cuttings are generally driven through the 
lower beds of the Chalk,* the same as those through which it 
is proposed to take the Channel Tunnel. There are hun- 
dreds of wells in the London district which penetrate more 
or less deeply into the Chalk. 
There is, therefore, abundance of information available as 
to the kind of work which must be undertaken. All these 
tunnels and cuttings are, however, driven above the sea- 
level, and similar works undertaken below the sea may meet 
with far greater difficulties. But this is not at all sure to 
be the case. The lower beds of chalk beneath the sea may 
contain no more water than those beneath the neighbouring 
shores. 
There are numerous cases in the mining districts, both of 
metal and coal, in which the workings are carried far out 
* Some of these were described in a Paper by Mr. S. HuaGues, ‘ On Chalk 
Excavations, and on the Means adopted under Different Circumstances of 
Intersecting the Great Chalk Ridges of England, for the Purposes of Railway 
and Canal Communication.” Civ. Eng. and Arch, Journ., vol. ii., p. 207, June, 
1839. 
