rOECE or THE AVAVES. 57 



and would weigh as much as a large three-decker. After these 

 great storms, salt pools are scattered here and there on the top of 

 the cliffs. 



The pressure exerted by these masses of water, hurled with such 

 impetus, is no less surprising. Thomas Stephenson ascertained that 

 the force of the sea dashed against the Bell Eock lighthouse amounted 

 to about 17 tons for every square yard. In the island of Skerryvore 

 the heaviest calculated pressure is about 3 tons and a half for every 

 yard, that is to say, more than 6^ lbs av. for every O'lG of a square 

 inch. With such a force the displacement of blocks which seem 

 enormous to us, is only child's play to the tempest waves. Before all 

 sea-ports, and roadsteads where great works, such as sea-walls and 

 breakwaters, have been constructed, seamen have been able to observe 

 the prodigious power of the angry water. On all the exposed works 

 at Holyhead, Kingston, Portland, Cherbourg, Port Yendres, Leghorn, 

 the waves have been seen to seize blocks weighing several tons, and 

 hurl them like playthings over the dikes. At Cherbourg the heaviest 

 cannon on the rampart have been displaced ; at Barra Head in the 

 Hebrides, Thomas Stephenson states that a block of stone of 43 tons 

 was driven more than If yards by the breakers. At Plymouth, a 

 vessel weighing 200 tons was thrown without being broken to the 

 very top of the dike, where it remained erect as on a shelf beyond 

 the' fury of the waves. At Dunkirk, M. Yillarceau has ascertained 

 by the most delicate measurements, that during a heavy sea the 

 ground trembles at nearly one mile from the shore. 



In the Gulf of Gascony, so frequently visited by tempests, the 



waves, coming from the west and north-west, are drawn into a sort 



of funnel, and hurl themselves against the shores with a force at 



least equal to that of the waves in the Channel, and the English seas. 



The works constructed by engineers to protect the roads and ports 



against this terrible pressure have been frequently swept away, 



or much damaged by the waves. Man must incessantly continue 



the strife he is engaged in with the sea, under pain of seeing the 



work of a century destroyed in a day. During the winter of 



1867 and 1868, M. Palaa says that blocks of masonry, 36 tons in 



weight, placed at the extremity of the dike at Biarritz, were thrown 



horkon tally from 11 to 13 yards ; one block was even raised nearly 



7 feet, carried over the breakwater, then thrown down, and rolled to 



a great distance during the storm. At St. Jean de Luz the surge is 



perhaps still more terrible, and some of the masses of stone now 



employed in constructing the dike of Socoa, at the entrance to the 



