482 MR MILNE ON THE GEOLOGY OF ROXBURGHSHIRE. 



In regard to what might have caused a current of 10 or 12 miles an hour, 

 Avhich seems sufficient, according to Mr HOPKINS, and according to the facts also 

 related by DE LA BECHE, for the transportation of boulders, various suggestions 

 have been offered. The most probable cause seems to be, a submarine eruption 

 to the west of Great Britain, of sufficient magnitude to produce a great wave. At 

 the time of the Lisbon earthquake in 1755, the focus of which is supposed to have 

 been about 100 miles to the westward, a wave was produced, which, when it 

 broke on the coast of Portugal, was from 40 to 60 feet high. This wave reached 

 the British Islands in about six hours, having travelled at the enormous rate of 

 about 150 miles an hour ; and on entering the different harbours in the south 

 shores of England and Ireland, broke the moorings of almost all the ships at 

 anchor. 



It is related by Sir WOODBINE PARISH, that during the earthquake which de- 

 stroyed Callao in 1678, the sea, after first retiring, rose with such violence as to 

 carry " three ships, about 60 or 100 tons," " over the town, which then stood on 

 a hill." 



" In 1746 Callao was again destroyed by an earthquake- wave, vast heaps of 

 sand and gravel occupying its position. All the ships in the harbour, except four, 

 foundered. One of these, a man-of-war, was found in the low ground of the Up- 

 per Chicara, opposite to the place where she rode at anchor, and near her the St 

 Antonio. Another of these vessels rested on the spot where before stood the Hos- 

 pital of St John, and the ship Succour was thrown up towards the mountains."* 



These accounts of the enormous size of the waves, which are formed during 

 many of the South American earthquakes, are fully corroborated by Mr CALD- 

 CLEUGH'S account of the earthquake, by which Talcahuano was destroyed in 1835. 

 There were several waves which then rolled in upon the land, apparently ex- 

 ceeding 40 feet in height. 



With reference to these cases, however, it deserves to be remarked, that they 

 prove only the power of moving water to move blocks, not to transport them, at 

 least for any considerable distance. The wave of translation referred to by Mr 

 HOPKINS, and as described in Mr SCOTT RUSSELL'S valuable papers on waves, pro- 

 duces only a momentary current at the place affected by the wave. There is a 

 forward propulsion of the aqueous particles only for a short distance, correspond- 

 ing with the width of the wave. The wave travels on, leaving behind it, the par- 

 ticles so moved. In like manner, a body immersed in the water, even of only the 

 same specific gravity with it, would be pushed forward but a short distance, and 

 left there. Of course, therefore, a block of granite, though it might readily be 

 moved, would not be transported more than a few feet by any single wave, how- 

 ever great in size or rapid in motion. 



* Abstract of Geological Society's Proeecdings for December 1835. 



