1872.) Geology of the Straits of Dover. 219 
boiled up with great force. On the contrary, above the 
water level, driftways were driven hundreds of feet in length, 
and left for months together without any timber shoring 
being required. It requires little imagination to perceive 
how great will be the pressure of water, and how immense 
the difficulties arising from it in the proposed Channel 
Tunnel excavated beneath 20 or 30 fathoms of water, 
and through a bed of hard chalk, doubtless abounding in 
joints and fissures. It has been the low level, 20 feet 
beneath that of the river, which has created the chief 
engineering difficulty and expense attending the sewerage 
works at Norwich.” 
If the foregoing description of the works at Norwich may 
be taken as a fair example of what would occur beneath the 
Channel, of course it is idle to think of driving a tunnel 
more than 20 miles long through such rocks, the whole of 
the water met with having probably to be raised to the 
surface by pumping. But there is no reason to think that 
the Chalk beneath the Channel will resemble this; rather is 
there every reason to think that it will be very different 
from it. 
In the first place we must remember that these Norwich 
works were in the Chalk-with-flints, wherein water is some- 
times abundant along certain lines. They were carried on 
very little below the river, and consequently any small joints 
or fissures would serve to convey the river-water down; 
whereas with a larger mass of rock above the works the 
joints and fissures might die out, or give place to others 
along different lines, and thus the water-channels would not 
be continuous. 
But there has been no proposal to carry a tunnel through 
the Chalk-with-flints. It is proposed to make it mainly, if 
not entirely, through the iower part of the Chalk-without- 
flints, which is not itself a truly permeable bed. Indeed, 
even if it were fully charged with water, as probably it 
would be, it would yield only a small quantity of that water 
from its own mass; almost the whole of the water met 
with in the tunnel would enter by joints and fissures. 
Joints and fissures in rocks are not formed as open cracks 
in the rocks; they become so by the incessant passage of 
water along them. Wherever water is passing through a 
jointed or fissured rock, especially if that rock be calcareous, 
it is gradually enlarging the cracks, and is rendering the 
passage of water more easy. But if the rock be beneath 
the sea, although it may be fully charged with water, this 
water may not, and probably would not, pass through it; hence 
