41 



the weather shore. The height of iinhroken waves, due to that fetch, 

 would be about 8 feet 3 inches ; but if the storm veered to W. or S.W., 

 the Irish coast would then form the weather shore, and the resulting 

 waves would be nearly twice as high. These are, of 

 course, unbroken waves in deep water, and not the 

 concentration or heaping-up of energy we see on a shelving beach 

 during an on-shore gale, dashing against cliffs and leaping into the air 

 100 feet high. 



At Skerryvore, a point on the west coast of Scotland, exposed to the 

 full fury of the Atlantic, waves were observed to exert a force of three 

 tons per square foot, and on the shores of the Shetland Islands, blocks 23 

 tons weight were transported by the waves a distance of 30 feet, and then 

 broken into fragments. 



In modern harbour-works advantage is taken of the employment of 

 large concrete blocks to resist the destructive force of the waves. Blocks 

 weighing 350 tons each are now employed with success. These are formed 

 on shore, and as each block becomes set or hard it is conveyed to its 

 destination in a barge provided with a derrick and jjowerful machinery, 

 by which it is lowered into position when the bed or substructure is 

 levelled to receive it. The advantage of employing such huge blocks is 

 chiefly that several linear yards of structure are laid in one operation, 

 reaching above low water mark, and capable of resisting the force of 

 the heaviest seas. Concrete, in the liqviid state, is also extensively employed. 

 In some instances it is formed in bags of 1 00 tons each, in others it is un- 

 protected and lowered in skips or boxes, the bottoms of which are provided 

 with butterfly doors, and opened by means of a trigger, worked from a 

 stage above water. The chief advantage of these modes of procedure is 

 that the concrete in the liquid state conforms readily to the natural bed 

 of the sea or substructure upon which it is deposited, thus dispensing 

 with the manual labour under water necessary in setting large blocks ; 

 and, further, the structure, when complete, is more monolithic, or 

 free from joints and weak places. 



Works in connection with tidal harbours, require to be even more 



