Sir Francis Fox, who dealt with the engineering aspects of
the scheme, described the character of the grey chalk, eighty- seven feet thick at Dover and seventy feet thick at Sangatte, through which the tunnels would be bored. It contained no flints, was apparently free from fissures or slides, and bad the peculiar quality of gradually "puddling" itself and becoming impervious. Even if fissures were encountered, they could be satisfactorily dealt with by high-pressure grouting. He estimated that the boring would occupy four years. After describing the system of ventilation and lighting and the precautions against fire, Sir Francis Fox finally dealt with the protection of the tunnel in case of war. There would be no question of destroying the tunnel. "All that would be necessary would be to open a valve and let in a certain quantity of water. Then nothing could pass through, not even a rat, and the water could not be got out before the declaration of peace."
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