416 EEPORT — 1882. 



(Section E, F, PI. VII.), down the centre of the Channel, shows the chalk 

 from where it begins, at the outcrop of the gault, dipping at first rapidly 

 beneath the sea, the dip gradually diminishing as we go eastwards. Now 

 the part of this section in which error is most likely to be found is in the 

 curve which denotes the base of the chalk near the outcrop. For the 

 curve showing the base of the chalk depends not only on the position of 

 the line on the map which shows the junction of the chalk and ganlt, 

 which is, probably, in the main, correctly plotted, but also on the line 

 which shows the junction of the two lowest beds of chalk of the French 

 geologists (Craie de Rouen and Craie Moyenne). It would be very rash 

 to take this last line as other than approximate ; yet all it could tell us, if 

 it were correctly plotted, would be the dip of the base of the chalk close 

 to the sea-bed, and, even to get that, we should have to assume the thick- 

 ness of the Craie de Rouen from its ascertained thickness on the two coasts. 

 Of the dip a short distance below the sea-bed we really know nothing, and 

 the curve indicating it must be imaginary. If the tannel is to follow the 

 lower beds of chalk it will have to be near this curve line ; and any varia- 

 tions in the curve will necessitate deviations in the line of the tunnel, so 

 that its length might be largely increased. This continual deviation of 

 line would add much to the difficulties of construction. Again, the lower 

 the beds in which the tunnel is placed, and the nearer to the outcrop of 

 those beds, the greater will be the risk of water finding its way along the 

 planes of bedding from the outcrop. 



As we pass from the outcrop of the base of the chalk and the gault, in 

 an easterly direction along the Channel, the chalk increases in thickness. 

 On Line No. 1, the chalk is 480 feet thick, while on Lines Nos. 2 and 3 it 

 is about half that thickness ; and, with the same thickness of chalk over 

 the tunnel, there would, on Line No. 1, be 245 feet more chalk below the 

 tunnel than on Lines Nos. 2 and 3. An error therefore which would 

 necessitate a considerable deviation in the line of tunnel on Lines Nos. 

 2 and 3 would not in any way affect No. 1 ; for it would require an error 

 altering the position of the whole mass of chalk, vertically 245 feet, to 

 disturb the tunnel line if made in direct line between Fan Hole and 

 Sangatte, that is on Line No. 1. (See Plates V. and VI.) 



I have given a third section across the Channel, along the line num- 

 bered 3 on the plan, and the position of a tunnel is shown on it in con- 

 tinuation of that shown on the section deposited by the South Eastern 

 Railway Company. This tunnel does not keep wholly in the lowest beds 

 of chalk, so that it does not fulfil the requii-ements which a tunnel begin- 

 ning to the westwards of Dover should. That it may do so, one of two 

 things must be done : the line of the tunnel shown on the plan must be 

 depressed some 130 feet so that it may follow the lowest beds across the 

 depression shown on the section, or we must bend the line No. 3 shown 

 on the plan more to the west, so as to follow the lowest beds of chalk, 

 where they are found at a higher level nearer to their outcrop. The first 

 course would render it impossible to make a drainage heading to the shore 

 in the chalk ; for the tunnel would be so low, at its lowest point, that it 

 would not be practicable to obtain a fall in the chalk to the shore. This 

 drainage heading has been already stated to be a necessity. The alternative 

 remains, but it would make the submarine tunnel at least one mile longer 

 than Line No. 3, which is already three miles longer than Line No. 1 

 from Sangatte. That is to say, to avoid passing out of the lowest 

 beds of chalk, the total length of tunnel would be increased by nearly 



