36 The Tunnel between France and England. 



the Chalk in the North of France, outcropped in the Boulonnais, 

 were again lost under newer formations near to the coast, and did 

 not reappear until the neighbourhood of Frome and Wells was 

 reached. But, although not exposed on the surface, they had been 

 encountered at a depth of 1032 feet at Calais, 985 feet at Ostend, 

 1026 feet at Harwich, and 1114 feet in London. They thus seemed 

 to form a subterranean table land of old rocks, covered immediately 

 by the Chalk and Tertiary strata. It was only at the southern flank 

 of this old ridge that the Jurassic and Wealden series set in, and 

 beneath these the Palaeozoic rocks rapidly descended to great depths. 

 Near Boulogne these strata were already 1000 feet thick ; and at 

 Hythe the author estimated their thickness might be that or more. 

 Supposing the strike of the Coal Measures and the other Palaeozoic 

 rocks to be prolonged from their exposed area in the Boulonnais 

 across the Channel, they would pass under the Cretaceous strata 

 somewhere in the neighbourhood of Folkestone, at a depth estimated 

 by the author at about 300 feet, and near Dover at about 600 feet, 

 or nearly at the depth at which they had been found under the 

 Chalk at Guines, near Calais, where they were 665 feet deep. These 

 Palfeozoic strata were tilted at high angles, and on the original 

 elevated area they were covered by horizontal Cretaceous strata, the 

 basement beds of which had filled up the interstices of the older 

 rocks as though with a liquid grouting. The overlying mass of 

 G-ault and Lower Chalk also formed a barrier to the passage of 

 water so effectual, that the Coal Measures were worked without 

 difficulty under the very permeable Tertiary and Upper Chalk of 

 the North of France ; and in the neighbourhood of Mons, notwith- 

 standing a thickness of from 500 feet to 900 feet of strata charged 

 with water, the Lower Chalk shut the water out so effectually that 

 the Coal Measures were worked in perfect safety, and were found to 

 be perfectly dry under 1200 feet of these strata combined. No 

 part of the Straits exceeded 186 feet in depth. The author, there- 

 fore, considered that it would be perfectly practicable, so far as 

 safety from the influx of the sea-water was concerned, to drive a 

 tunnel through the Palaeozoic rocks under the Channel between 

 Blanc Nez and Dover, and he stated that galleries had actually been 

 carried in coal, under less favourable circumstances, for two miles 

 under the sea near Whitehaven. But while in the case of the 

 London clay the distance seemed almost an insurmountable bar, here 

 again the depth offered a formidable difficulty. As a collateral 

 object to be attained, the author pointed to the great problem of 

 the range of the Coal Measures from the neighbourhood of Calais in 

 the direction of East Kent, which a tunnel in the Palaeozoic strata 

 would help to solve. These were, according to the author, the 

 main conditions which bore on the construction of a submarine 

 tunnel between England and France. He was satisfied that on 

 geological grounds alone, it was in one case perfectly practicable, 

 and in one or two others it was possibly so ; but there were other 

 considerations besides those of a geological nature, and whether or 

 not they admitted of so favourable a solution was questionable. In 



