1872.] Geology of the Straits of Dover. 209 
The various schemes proposed are of three classes *:— 
a Bridge over the sea, a Tube on the bed of the sea, anda 
Tunnel beneath the bed of the sea. With the second of 
these, or the tube scheme, Geology has nothing to do. 
Concerning the first, there is the important question of 
foundation, upon which-a geologist’s opinion might be 
sought; but whether the answer were favourable or other- 
wise would but little affect the project. It is a question 
which can easily be settled by actual experiment, at compa- 
ratively little cost; and even if a good foundation were hard 
to find (an improbable supposition), engineers would be at 
no loss to make one: the question is solely one of expense. 
With the third scheme, that of tunnelling, the case is 
very different. Here nearly all the questions which arise at 
the outset are such as can only be fully appreciated by one 
having some geological knowledge; they are, chiefly, the 
depth and thickness of the various rocks beneath the 
Channel, their extent, physical characters, permeability, &c. 
Perhaps in the present state of the question we shall be 
doing some service by (1) briefly narrating what is actually 
known of the geological structure of the coasts bordering 
the Straits of Dover; (2) by enquiring what help this 
knowledge affords us towards ascertaining the actual con- 
dition of the sea-bed ; and (3) by testing the various tunnel 
schemes by the data thus obtained. 
The physical geography and geological structure of the 
opposite coasts of the Channel have so many characters in 
common, that a description of one side will in great part 
serve for that of the other. There are, however, some 
points of difference which are of great importance in this 
question. . 
The most striking features of the Straits of Dover are the 
Chalk cliffs, rising steeply from the shore, of great height, 
and of dazzling whiteness. The similarity in the appearance 
of these cliffs led many old writers to speculate on their 
vol. v., 1st series and vol. iv., 2nd series ; the Statement of the Executive Com- 
mittee of the Channel Tunnel, with Engineer’s Report and Diagram (1869). 
The thicknesses of the oolitic rocks in the Bas-Boulonnais are taken from a 
Paper by M. Ricavux, in Bull. Soc. Acad. de Boulogne (1865) ; the geology of 
the Bas-Boulonnais is partly from a Map by M. pu Sourcu, and partly from 
original observations. A detailed account of the strata passed through in the 
Calais Well is given by Mr. Mackie in the Geol. and Nat. Hist. Repertory, 
vol. i., p. 122: this is taken from a table and specimens preserved in the 
Museum at Calais. . . 
* The proposal to constru@ large ferry-boats which will convey trains of 
carriages over the Channel does not concern us here. 
VO. 1...(N-S:) 2E 
