40 REPORT—1850. 
on the beach, to which I have given the name of the forced sea-wave (Dy- 
namics of Earthquakes, Trans. Roy. Ir. Acad.), is mentioned. 
Thus Darwin (‘Journal of a Naturalist’) says, “In almost every severe 
earthquake the neighbouring waters of the sea are said to have been greatly 
agitated ; the disturbance seems generally, as in the case of Concepcion, to 
have been of two kinds: first, at the instant of the shock the water swells 
high up on the beach with a gentle motion, and then as quickly retires ; 
secondly, some time afterwards the whole body of the sea retires from the 
coast and then returns in waves of overwhelming force.” ‘“ During most 
great earthquakes, and especially in those on the west coast of America, it is 
certain that the first movement of the waters has been a retirement.” 
Some authors have attempted to account for this by assuming that the 
water retains its level, while the land is suddenly elevated or thrown up 
out of it and again dropped down to its former level; but Darwin well 
says, “surely the waters close to land, even of a steep coast, would here 
partake of the motion of the land.” Darwin views this secession of the 
water as due to the first action of the great sea-wave formed or forming far 
out at sea. J have, on the other hand, endeavoured to show that it is due 
to the traversing along under the sea of the crest of the earth-wave of shock, 
which moves so fast as to force up a low broad unbroken ridge of water 
vertically over it, which is imperceptible while the earth-wave is moving 
under deep water, but becomes visible as it approaches the shallow shore ; 
and the effect of the sudden coming in to land, of this earth-wave, carrying 
the forced sea-wave as it were on its back, is, that at the moment they part 
company upon the beach, the beach itself is for the instant elevated to the 
height of the earth-wave and as instantly dropped again, so that slipping from 
under the sea, the earth-wave gives to the sea for the moment the appearance 
of having retired and again advanced to its former level. (See Dynamics of 
Earthquakes, p. 18, 20.) In this Report upon the facts of Earthquakes, it 
would be out of place to do more than refer to my memoir above alluded to 
for more detailed speculations of the subject. 
Combinations analogous to those which f suppose produce the forced sea- 
wave, will also account for those strange movements of distant lakes, islands, 
rivers, &c. recorded as occurring in connexion with distant great earthquakes. 
Thus may be produced the oscillations often observed in inland lakes far 
removed from the convulsed centre, as in the highland lakes of Scotland, on 
occasion of the great Lisbon earthquake, and of the South Carolina earth- 
quake of 1811, when the course of the Mississippi was temporarily arrested 
below New Madrid; or as in the Calabrian earthquake, where the course of 
the river Metramo was thus momentarily stopped, and then began again 
to run; in the latter cases the crest of the earth-wave, bearing a forced wave of 
water over it, having run up stream like a moving subaqueous or partial 
dam across the river. 
But a far more striking phenomenon is THE GREAT SEA-WAVE which 
so often rolls in upon land at the conclusion of great earthquakes. 
This has never been observed to take place in any earthquake whose 
centre of impulse was inland, however violent. Thus in the Calabrian earth- 
quake there was no great sea-wave, for the great wave that swept the mole 
of Messina and drowned the Prince of Scilla and many thousands of his 
people, was produced by the sudden fall into deep water of an enormous 
mass of rocky mountain close at hand, detached by a shock. On the other 
hand, wherever the origin has been at sea, and especially in the great South 
American and in the Lisbon earthquakes, an immense rolling wave has come 
in shore some time after the shock has been felt, and this has travelled in 
