4 PROFESSOR T. MCKENNY HUGHES, M.A. 



upon the coast, and explain how caves must everywhere 

 be formed where shattered or softer rock is exposed to the 

 lash of the wind-driven sea. 



But this is not all. The wave picks up great boulders and 

 hurls them at the rocks that bar its advance. It is quite common, 

 after a storm, to find large stones lodged on a promenade or 

 pier, where they must have been caught up in the wave and 

 thrown upon the land. Stones are always carried forward up 

 an incline as far as the waves advance ; but the cases I refer 

 to now are those in which the stone has been thrown up to 

 the top of a vertical wall. The last place I remember having 

 seen this was in a great storm a few years ago at Hunstanton. 

 The same thing takes place on a grand scale on some of the 

 wild, rocky cliffs of North-Western Scotland, for instance. 

 The Director-General of the Survey has described how in 

 storm, great blocks are hurled up on to the top of the cliff 

 near the Old Man of Hoy. 



The force of the Atlantic waves at the Skerryvore Rocks, 

 as estimated by the marine dynamometer, an instrument 

 designed by Thos. Stevenson for this purpose, was found to 

 be as much as 6,083 Ib. to the square foot.* 



From the height to which the spray was thrown, he inferred 

 a pressure of about 3 tons to the square foot ; and farther 

 recorded that a block of stone, estimated at 48 tons in weight, 

 " was seen to move under the influence of each wave."f 



" On the Bound Skerry of Whalsey, which is only exposed to the waves 

 of the North Sea or German Ocean, he had found .... masses of rock 

 weighing 9 tons and under, heaped together by the action of the waves at 

 the level of no less than 62 feet above the sea ; and others ranging from 6 

 to 13j tons were found to have been quarried out of their positions in situ, 

 at levels of from 70 to 74 feet above the sea. Another block of 7 T 7 ff tons, at 

 the level of 20 feet above the sea, had been quarried out and transported to 

 a distance of 73 feet .... over opposing abrupt faces as much as 7 feet in 

 height." (J) 



It is clear that such waves and such boulders would make 

 short work of broken rock or a rotten dyke, and any old 

 cave or fissure opened out by the sea would not be likely to 

 have much of the original deposits left in it. The first storm 

 would clear out all earth and bones, and leave in its place 

 only the well-worn pebbles of a rocky shore the battered 

 shot of nature's great marine artillery. A sudden upheaval 

 would leave the cave either quite clear, if it was on a clean, 



(*) Stevenson, Thos. Edin. New Phil. Jour, xlviii. 1850, p. 41, 

 (+) Ditto, Proc. R. <S'oc. Edin. vol. ii. 1844-50, p. 13. 

 (J) Ditto, Proc. E. Sot. Edin. vol. iv. 1862, p. 200. 



