THE CHANNEL TUNNEL. 
399 
not be room for tunnelling. The tunnel must rise from the 
ends towards the centre, and the Grault would not allow of this, 
unless the tunnel were curved, rising from either shore obliquely 
to the rise of the beds. But we must allow for the possible 
existence of small faults ; and a fault which in a thick bed 
would be of very small consequence might be sufficient to throw 
the Grault out of the line altogether, and this would be a very 
serious matter. 
The Kimeridge Clay has not hitherto attracted much atten- 
tion as bearing upon this question. In some of the early 
tunnel-schemes it was proposed to commence the work in the 
Kimeridge Clay of the French coast and to carry it westwards 
into the Cretaceous or Wealden Beds of the English coast. In 
those days the succession of strata beneath the Weald was quite 
unknown, and it is only during the present year that the pro- 
gress of the Sub-Wealden Boring has made us, to some extent, 
acquainted with it. The boring is still incomplete, but some 
important additions to our knowledge have already been made. 
We now know that beneath the Purbeck Beds there are the 
Portlands, and beneath these again there is a thick mass of Kime- 
ridge Clay.* The succession of beds, as yet proved at the 
boring, is as follows : — 
Feet 
Purbeck Beds. Shale, impure limestone, and gypsum 180'0 
Portland Beds. Shale, sand and sandstone, with no-l 110 0 
dules of chert . . . J 
Kimeridge Clay. Clay and shale ; sometimes slightly ^ 
sandy and calcareous, with bands L about 67(H) 
of cement-stones in the lower part ) 
Oxford Clay. Dark clay j with hard sandy bands . about 53-0 
10130 
Seventeen feet more have been bored, making a total of 1,030 ft., but the 
lowest cores are not yet drawn. 
Although the Kimeridge Clay contains some bands of cement- 
stone, yet there is no reason to doubt that the whole mass is 
practically impervious to water. The diamond system of boring 
brings up long unbroken cores of the strata passed through, 
and enables us to judge with perfect accuracy of the mineral 
character of the beds. The cores are always wet on the outside, 
from the water which fills the hole, but when the more massive 
pieces are broken across, they are generally found to be quite 
dry inside. Judging, then, from the evidence which the boring 
supplies, it would seem that a tunnel could be driven through 
the Kimeridge Clay with little or no trouble from water. 
On the French coast the Kimeridge Clay is thinner, and 
* The suitability of the Kimeridge Clay for the Channel tunnel has been 
noticed by Mr. Henry Willett, but the subject has not yet received the at- 
tention which it deserves. 
