60 



TflE SEVERN TUNNEL. 



When the centre line had been decided upon, vei-y nu- 

 merous additional soundings were made upon that line, so 

 that ultimately they -vrere hardly two feet apart all the 

 way across ; yet in no place was any fissure fouiHl : l)ul; the 

 bottom was ridged, something like the ridge and furrow 

 of a ploughed field, as might have been expected from tlie 

 nature of the wtiaring away, by gravel running longitudi- 

 nally up and down. 



The permanent centre lino of the Tunnel was now fixed 

 and set out, and the surveys made on both sides of the 

 river. 



Wliere the Tunnel emerged inshore, deep and extensive 

 cuttings had, of course, to bo made on both sides of the 

 river. These cuttings, at tlic gi'adient of 1 in 100, ran for 

 a long distance before they got above high-water level^that 

 on the English side, being sixty feet below the Severn 

 alluvinm, had to bo carried 6,000 feet through the Severn 

 Marsh before it got out of cutting, and involved heavy 

 bridges and other works to carry the roads and streams 

 across it. But it also involved another important work, as 

 may now bo explained. 



From some facts he had before observed, it became plain 

 to the writer of this paper that it would be absolutely neces- 

 sary to make high, sea-banks round the tunnol-mouth 

 cuttings on both sides of the river, because the present sea- 

 banks by the river side are not high enough to keep out 

 very high, and exceptional floods, which must occur when 

 great storms tiike place upon very big spring-tides. His 

 attention was first called to this subject in a striking manner 

 soon after the opening of the Ferry llailway in 18G3. 



On the occasion aJlnded to, there was a great gale of 

 wind from the South- West, accompanied by a low barometer. 

 It occurred on a spring-tide, though not a very big one, and 



