The Tunnel between France and England. 35 



a view to serve as data for any future projects of tunnelling, and to 

 show in what directions inquiries should be made. The points con- 

 sidered were the lithological characters, dimensions, range and 

 probable depth of the several formations. The London-clay, at the 

 mouth of the Thames, was from 200 feet to 400 feet thick, while 

 under Calais it was only 10 feet, at Dunkirk it exceeded 264 feet, 

 and at t)stend it was 448 feet thick. He considered that a trough 

 of London clay from 300 feet to 400 feet, or more, in thickness, ex- 

 tended from the coast of Essex to the coast of France, and, judging 

 from the experience gained in the Tower Subway, and the known 

 impermeability and homogeneity of this formation, he saw no diffi- 

 culty, from a merely geological point of view, in the construction of 

 a tunnel, but for the extreme distance — the nearest suitable points 

 being 80 miles apart. The Lower Tertiary strata were too unim- 

 portant and too permeable for tunnel work. The Chalk in this area 

 was from 400 feet to 1000 feet thick ; the iipper beds were soft and 

 permeable, but the lower beds were so argillaceous and compact as 

 to be comparatively impermeable. In fact, in the Hainault coal- 

 fields they effectually shut out the water of the water-bearing 

 Tertiary strata from the underlying Coal Measures. Still, the 

 author did not consider even the Lower Chalk suited for tunnel 

 work, owing to its liability to fissures, imperfect impermeability, 

 and exposure in the Channel. The Gault was homogeneous and im- 

 permeable, but near Folkestone it was only 130 feet thick, reduced 

 to 40 feet at Wissant, so that a tunnel would hardly be feasible. 

 The Lower Greensands, 260 feet thick at Sandgate, thinned off to 50 

 feet or 60 feet at Wissant, and were all far too permeable for any 

 tunnel work. Again, the Wealden strata, 1200 feet thick in Kent, 

 were reduced to a few unimportant rubbly beds in the Boulonnais. 

 To the Portland beds the same objections existed as to the Lower 

 Greensands, both were water-bearing strata. The Kimmeridge-clay 

 was 360 feet thick near Boulogne, and no doubt passed under the 

 Channel, but in Kent it was covered by so great a thickness of 

 Wealden strata as to be almost inaccessible ; at the same time it 

 contained subordinate water-bearing beds. Still, the author was of 

 opinion that, in case of the not improbable denudation of the Port- 

 land beds, it might be questionable to carry a tunnel in by the 

 Kimmeridge-clay, on the French coast, and out by the Wealden beds 

 on the English coast. The Oolitic series presented conditions still 

 less favourable, and the lower beds had been found to be water- 

 bearing in a deep Artesian well recently sunk near Boulogne. The 

 experimental deep boring now in progress near Battle would throw 

 much light on this part of the question. 



The author then passed on to the consideration of the Palgeozoic 

 series, to which his attention was more particularly directed while 

 making investigations, as a member of the Koyal Coal Commission, 

 on the probable range of the Coal Measures under the South-East of 

 England. He showed that these rocks, which consisted of hard 

 Silurian slates, Devonian and Carboniferous Limestone, and Coal 

 Measures, together 12,000 feet to 15,000 feet thick, passed under 



