On the geological conditions affecting the construction of a tunnel between England and France / by Joseph Prestwich ; with an abstract of the discussion upon the paper ; edited by James Forrest.
- Joseph Prestwich
- Date:
- 1874
Licence: Public Domain Mark
Credit: On the geological conditions affecting the construction of a tunnel between England and France / by Joseph Prestwich ; with an abstract of the discussion upon the paper ; edited by James Forrest. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![land springs; (2) the prohahie occmrence of faults or fissures; and (3) the dangers of leakage through the exposed Chalk at the bottom of the Channel. Preference was given to the Pahnozoic rocks. No alarm was experienced at the idea of tunnelling through Silurian slates, or Devonian or other lime- stones ; and there was evidently a lingering notion that coal might be extracted during the progress of the tunnel. That was, no doubt, a tempting prospect,—the idea of realising 405. a ton for the excavated materials. But the practical question was, what further explorations should be made? Considering the length of a tunnel through the clay, and the evidently great but uncertain depth of a tunnel through the Palasozoic rocks, the safe and middle course seemed to be a further explo- ration, as had been proposed, through the Lower or Grey Chalk. Land springs might prove an obstacle; but these would be found at the commencement of the work, and before any serious expense had been incurred. With regard to leakage, any one who knew much of the Lower Chalk would be pretty well con- vinced that the impermeability of the argillaceous Chalk Marl at a considerable depth was so great as to afford every probability of success, if only drift waj’-s were successfully pushed in the first instance to a distance of ^ a mile from the land on each side. There was, of course, a possibility of meeting with faults or fissures ; but there was also a probability that they would be completely choked up by material as impermeable, at the depth of the tunnel, as the Grey Chalk itself. It appeared to him that the prospect of success was sufficient to justify an attempt at boring through the Chalk from each side of the Channel. It was hardly possible, indeed, to test the problem in any other way. The difficulty and expense of boring vertically through the water in the Channel would be considerable; a number of such bore holes would be necessary in order to afford any degree of certain information; and they might, even if they were carried out, cause mischief by creating, so to speak, the very fissures which it was so desirable to avoid. All must admit the necessity for an improvement of the present means of communication across the Channel; and those who were in favour of a tunnel should not consider as rivals any other schemes having that object in view. There were three or four hundred thousand persons erossing every year, in spite of the inadequate facilities afforded for the passage, and in spite of the disturbed weather that prevailed for three quarters of the year. These numbers would soon be doubled if the facilities for crossing were increased; and it was to be hoped some of the [1873-74. N.S.] E](https://iiif.wellcomecollection.org/image/b2244614x_0053.jp2/full/800%2C/0/default.jpg)
