Mr. Matuer on the Dynamics of Karthquakes. 67 
that thus the retreat of the water is only apparent, and due in reality to the pre- 
vious rise of the land.* 
It is scarcely necessary to refute these hypotheses at length: as to the first, 
granting such a cavity under the deep sea to be suddenly filled, it would pro- 
duce no immediate sensible effect on the distant shores, and if it ever produced 
any, it would be a swell rolling in subsequently, and not a recession at the 
moment of shock. 
The second hypothesis is one of those samples of geology run wild, by which 
if only a sufficiently monstrous postulate be granted, anything may be accounted 
for. 
Nor, lastly, is the reviewer of Lyell in the Quarterly Review, No. lxxxvi. p. 459, 
more fortunate in his explication. He says: “ If a portion of the bed of the sea 
be suddenly upheaved, the first effect will be to raise over the elevated part a 
body of water, the momentum of which will carry it much above the level it will 
afterwards assume, causing a draft or receding of the water from the neighbour- 
ing coasts, followed immediately by the return of the displaced water, which will 
also be impelled by its momentum much further and higher on the coast than its 
former level.”’ 
This last view rests upon a mistaken notion of the mechanical conditions of 
the question. There is not the smallest evidence, that a wave produced far 
away at sea over acentre of disturbance, would produce any withdrawal of water 
at the instant from shores often distant by hundreds of miles, and, moreover, 
this theory allows no time for the earth wave or shock itself, produced under such 
conditions, to reach the land, which it is observed to do, at the instant of the reces- 
sion of the water. 
Mr. Lyell himself offers no solution, nor have I been able to find one else- 
where; I believe, therefore, that the explanation I am now about to give, for 
the first time, renders a true account of the phenomena, and, like all truth, 
when once grasped, will be found fertile in shewing the way to further and more 
advanced knowledge. 
First, then, in almost all great earthquakes it is admitted the shock comes 
from the sea. Let us assume a centre of disturbance far from land, below the 
* Michell’s Phil. Trans., vol. li. p. 614. 
K 2 
