FOR GREA T BRITAIN AND IRELAND. 63 



Even in the previous winter a huge mass of stone near sea- 

 level was pointed out by an intelligent under officer of the 

 lighthouse, which stone had been wrenched out of its 

 bed, and moved up an incline of IO D or 12 to a distance of 

 1 6 feet; and with this proof," says Mr. Stevenson, "all 

 scepticism vanished." 



In his article on Harbours in the * Encyclopaedia Britan- 

 nica,' Qth edition, 1883, Mr. T. Stevenson records the over- 

 throw of a concrete block of 1350 tons, at Wick, in 1872, and 

 of another block containing 1 500 cubic yards of material, 

 overthrown in 1873. Foundations of 18 feet below low water 

 have been washed out, and the bottom excavated 15 feet 

 lower than this by the volume of the sea. This last-named 

 block of concrete was estimated to weigh 2600 tons. 



By the erection of dynamometers at Skerryvore, 

 Dunbar, and Buckie, it was ascertained "that a force 

 equivalent to 3^- tons per square foot, however much more, 

 was excited by waves under extreme circumstances ; that 

 this force does not act by a sudden finite impact like a 

 cannon-ball, but is continuous during the period that the 

 disc of the dynamometer is immersed in the passing wave. 

 In short, to make the cases analogous, it is like a con- 

 tinuous succession of cannon-balls." 



OF CAUSES WHICH AFFECT THE FORCE OF WAVES, 

 AND THE FACT THAT THE TIDES IN MANY 

 CASES ACT AS BREAKWATERS TO THE SHORE. 



At not a few points of many coasts a heavy breaking 

 sea is met with, even in fine weather ; such breakings of 

 the waves are termed by seamen, races, or roosts, or 

 overfalls ; thus we have the Race of Portland, the Race of 



