THE CHANNEL TUNNEL. 415 



a rise of tide of 40 feet, and a deptli of water at high water of 90 feet in 

 the deepest part of the channel. It passes, for a considerable portion of 

 its length, through the Triassic red marl, which has many points of 

 resemblance to the chalk. The marl, which is in nearly horizontal beds, 

 is mnch fissured, and from these fissures, as well as from spaces between 

 the planes of bedding, mnch water is discharged. At the English end of 

 the submarine part of the tunnel, for some distance, there is only from. 

 35 to 40 feet of this open-jointed red marl above the brickwork of the 

 tunnel, which is already finished where the cover is thinnest. Salt water 

 flows freely into the work ; and, to show how the water-channels are dis- 

 connected, salt and fresh water have, in some cases, flowed from adjoining 

 fissures, and the fresh water has been allowed to flow, for drinking pur- 

 poses, through pipes built into the brickwork. The largest quantity of 

 water has been met Avith on the land portion of the tunnel ; and the largest 

 spring met with was in the land tunnel. It discharged 5,000 gallons a 

 minnte, and burst suddenly into a heading, which had been driven for 

 over 1,000 feet, in millstone grit, without meeting with any water. If the 

 heading had been driven at a level of 10 feet lower, the spring would have 

 been avoided in the heading, but would have been met with when it was 

 enlarged to the full size of the tunnel. The total quantity of water now 

 being pumped is between 7,000 and 8,000 gallons a minute. 



The examples I have given show that engineering works need not be 

 stopped, even by large quantities of water ; and, mnch as we know of the 

 chalk and its water-bearing qualities, there is nothing to show that water 

 would be met with in such large quantities as to stop tunnelling, even in 

 the upper chalk with flints. 



A tunnel can be made from Fan Hole, in a direct line to the French 

 coast, wholly in the upper part of the lower chalk without flints, as will 

 be seen from the section of Line No. 1 of the Plan, PI. V. ; but, as has 

 been already stated, a tunnel could be made from the same place, if it 

 were advisable, for nearly three-quarters of the whole distance, in the 

 lowest beds of grey chalk. To do this, it would be necessary to curve 

 the line of tunnel southwards, after leaving the shore, and then east- 

 wards, as shown on the plan in Line No. 2, PI. V. This Avould make the 

 sea tunnel nearly 1^ miles longer on Line No. 2 than on Line No. 1, PI. V. 

 That is, the certain immediate cost of making 1^ miles of tunnel with 

 the prospective disadvantage of 1^ miles more sea tunnel, to work, main- 

 tain, and ventilate, would be incurred, to save the cost o? possihle excess 

 of pumping on the one route over the other. 



"Whatever may be urged as the advantage of attempting to follow these 

 lower beds, there are some very obvious disadvantages and positive dangers 

 in attempting to do so. 



In the beginning of these discussions respecting the tunnel line, certain 

 questions were given as necessary for consideration. Of these, the third 

 was : — On what line will an error in our geological calculations be of least 

 moment to our tunnelling operations? The map and sections, to which I 

 have referred, are all based on the result of the French Company's work. 

 The marine and geological survey was made with care and precautions 

 such as were probably never before taken, and is an admirable piece of 

 work. As long as it deals with the surface of the sea-bottom, the reports 

 and accompanying plans and sections probably tell us a true story, on 

 which we may rely. But when we pass from the surface of the sea-bed to 

 the strata beneath, we go from facts to conjectures. A longitudinal section 



