﻿of the Sea not produced by Winds or Tides. 37 



thus accompanied in all parts of the world, whether on sea-coasts 

 or in lakes, distinguished authors on both sides of the Atlantic 

 have ascribed them (when unaccompanied with known earth- 

 quakes) to storms or unusually great and sudden augmentations 

 or diminutions of the atmospheric pressure on the surface of the 

 water. But this hypothesis is quite at variance with known facts, 

 and so are all the other hypotheses hitherto advanced by geolo- 

 gists, as I have shown in the printed Transactions of this Society 

 and elsewhere. 



My attention was first drawn to this subject by having wit- 

 nessed one of these disturbances in Mount's Bay more than 

 twenty-five years since, which I described first in a letter printed 

 in the Literary Gazette of the 15th of July, 1843, and after- 

 wards more fully in the paper which I read before this Society 

 in the same year. During this long period every fact I have 

 met with connected with the subject confirms me in the opinion 

 that the hypothesis which I then, and in subsequent years, sub- 

 mitted to this Society is the only one capable of reconciling all 

 the observed facts — that hypothesis being that all these extra- 

 ordinary agitations (of which each efflux, as well as each influx, 

 occupies generally about five minutes, and never more than ten 

 on our coasts) are produced by local submarine shocks of earth- 

 quakes without any upheaving, subsidence, dislocation, or frac- 

 ture of the submarine ground. The way, too, in which they are 

 produced on shores or submarine ground sloping outward, I 

 have also fully explained, viz. by the continually repeated dash- 

 ings seaward of the surface of the water by the vertical and rapid 

 vibrations of the submarine ground, until a very broad, but not 

 high, wave is raised, and much of the shore is consequently left 

 dry. When the vibrations have ceased, the dashed-off waters 

 return shoreward to find their level, and move up and down on 

 the shore like a pendulum until the equilibrium is restored. 

 That a shock does generally consist of a rapid succession of 

 countless vibrations is evident, not only from its being felt at 

 sea "like the letting out of a cable," and on land "like a wagon 

 rushing over a paved road," but by its very names of earthquake, 

 tremblement de terre, and seismos. 



These tide-like movements of the sea are totally unlike the 

 agitations produced by storms. Of these latter agitations we 

 had a memorable example on the 24th of April last at the Scilly 

 Isles and along the southern coasts of Cornwall and Devon, when 

 the waves rose so enormously, and their spray ascended to such 

 an unusual height, that no one who witnessed the spectacle can 

 ever forget it. The master of the Great Western Docks in Mill- 

 bay, Plymouth, informed me that, as the huge waves rolled in 

 and the vessels outside the docks mounted over them, great parts 



