Mr. Mauer on the Dynamics of Earthquakes. 71 
immediately below it, this latter elevation travelling with such immense velocity, 
that the hillock of water pushed up above it has not time to flow away laterally, 
and reassume its own level. 
Thus, then, the earth wave below, when in shallow water, is attended by a 
small forced sea wave, vertically over it, upon the surface of the sea, and these 
two reach the inclined beach or shore at the same moment; but as the beach 
is so inclined, and the forced sea wave, as well as the earth wave, are long and 
flat, and the velocity of the latter very great, the earth wave, as it were, slips 
from under the forced sea wave, at the moment of reaching the beach, which it 
for the moment elevates, by a vertical height equal to its own, and as instantly 
lets drop again to its former level. (See Plate II. Fig. 4, and m.) 
There is thus an apparent small recession of the sea from the shore, at the 
moment of the shock, followed almost directly by its flowing up something higher 
than the usual tide-mark, as the forced sea wave now breaks, and expends itself upon 
the shore. It is this forced sea wave, also, that communicates the earthquake 
shock to ships at sea, as if they had struck upon a rock. When, however, a ship 
is so struck in very deep water, as in the case of the Winchelsea, on the passage 
home from Bengal, in latitude 52° N., longitude 85° 33’ E., hundreds of miles from 
land, we may conclude that the centre of disturbance is either directly under the 
ship, or very near, and that the shock felt is the actual earth wave shock, trans- 
mitted vertically or diagonally upwards, like a blow, through the deep water.* 
It is possible that the aqueous sound wave may communicate a vibratory 
jar to a ship afloat in the water through which it passes, but not the shock uni- 
versally described as like striking on a rock, and often mentioned as violently 
straining the timbers of the ship. 
This, I believe, is the true explanation of the small apparent recession of the 
sea, just at the moment of the shock; and combinations analogous to this will 
account fully for all the strange movements of distant lakes, islands, rivers, 
&c. &c., recorded as occurring during great earthquakes. The earth wave, for 
instance, of the Lisbon earthquake, when it had reached Scotland, and passed 
under the Highland lakes, must have produced similar phenomena of oscil- 
lation in the waters on their shores; and in passing under the bed of a river, in 
* Quarterly Journal, vol. xvi. p. 184. 7 Ibid. vol. xvii. p. 43. 
