THE CHANNEL TUNNEL. 
401 
that- this amount is comparatively small. In works, such as 
breweries, &c., where large quantities of water are required, 
galleries are often driven through the Chalk in hopes of reaching 
fissures which may yield a good supply. But in no case is more 
water found than can readily be pumped up ; and there is no 
reason to suppose that more water would be met with in 
the tunnel than could be kept under by powerful pumps. The 
water-bearing fissures will be encountered separately, and most 
of them can be separately dealt with. Sir J. Hawkshaw has 
stated that in the drainage-works at Brighton a tunnel 5 J miles 
long has been constructed. This, being through the Upper 
Chalk, and only a short distance below the sea-level, has yielded 
a large quantity of water ; 10,000 gallons per minute have been 
pumped, by engines of 150 horse-power; but in the Channel tun- 
nel provision has been made for engines of 2,000 horse-power. 
The ordinary water-bearing fissures of the Chalk need not 
therefore cause us any alarm. We need only consider the pos- 
sibility of encountering large open faults, fissures, or pot-holes, 
communicating with the sea. Prof. Eamsay, in the course of 
the discussion on Prof. Prestwich’s paper, called attention to 
the possible existence of pot-holes filled with sand and gravel, 
such as are well known over the surface of the Chalk. If these 
exist under the bed of the Channel and continue downwards to 
the lower beds of Chalk, they may offer serious obstacles to the 
work. But, on the land, we find that they generally occur 
over the Upper Chalk ; they rarely penetrate downwards so far 
as the Lower Chalk; and, as the Chalk now beneath the Channel 
has been there for long ages, protected from the sub-aerial ac- 
tion which causes pot-holes, we may expect that such obstacles 
are not likely to occur along the proposed line of tunnel. 
Again, as to faults ; it is almost certain that in a tunnel 23 
miles long many faults will be met with, but there is no reason 
to suppose that any one of them will yield an overpowering 
quantity of water. The coal mines of Durham, Northumber- 
land and Cumberland, are carried well under the sea ; faults are 
cut in the workings, which give no more trouble than those 
under the dry land ; often, indeed, they give much less, for the 
quantity of water met with does not depend upon whether the 
works lie under sea or land, but mainly upon the water-bearing 
qualities of the rocks which lie above the coal. It has been 
suggested that probably there is a great fault or fissure in the 
Channel to which the Straits of Dover owe their origin ; but of 
this there is no evidence whatever. Even if such a fault 
occurred it might be closed with clayey matter, and so cause 
no great inconvenience. In coal-mining the faults met with 
are numerous enough, but they do not generally very greatly 
increase the quantity of water ; they never yield more water 
VOL. XIII. NO. LIII. D D 
