THE SEVERN TUNNEL. 



51 



great bank of sand wliicli liad been deposited there by the 

 flood-tide, and at that time formed part of the Dun Sand, 

 This is the reason why deep water is always to be found 

 there for tho Ferry Passage. Tliis process is repeated 

 during every spring-tide, as the writer liad reason to know ; 

 for on one occasion, in measuring and sounding across this 

 channel, tlio bow of the boat wa,s run aground upon the Dun 

 Sand : tho man at the bow jumped out and shoved tire boat 

 off again. In doing so, ho made two steps on the sand ; but 

 the third, from which he meant to spring on board again, 

 went into deep water, a,nd ho would have disappeared alto- 

 gether, had ho not held hard to the boat. It was found 

 that the sand was being washed away so fast that it formed 

 an upright face deeper than the length of an oar. This fact 

 was afterwards frequently observed during ebb-tide. The 

 Ferry channel there is wasliod to a depth of 42 feet below 

 the lowest water of a spring-tide. 



The Dun. Sand, without doubt, joins on to tho English 

 Stones during the flow of the big spring-tides, and the Fori'y 

 cliannol is washed clear again by the English lake current 

 every time at lialf-ebb. This proves the enormous quantity 

 oisand that is moved during every one of these big -tides. 



Then, as to tho quantity of gravel moved during such tides, 

 Ihoi'o wiis a good illustration when the foundations of the 

 I'ortskowet Pier were being got in. A base of brickwork, 

 four feet deep, had to be put in to form a footing to which 

 the framed wooden logs of the viaduct were to be bolted. 

 When the men got to tlioso near the low-water mark, it 

 had to be put in dui'ing tlio low water of big spring-tides, 

 ilnd they found much trouble in excavating a level founda- 

 tion for tho brickwork out of tlie very li;ird marl, by i-eason 

 of tlie largo quantity of very coarse gi'avel that every tide 

 washed into the excavation ; so that some time was always 



