Mr. Mauuet on the Dynamics of Earthquakes. 17 
into the conditions of this peculiarity of tide waves; enough has been stated 
to. show that a single shock, or earth wave, may be succeeded either, first, by 
one great sea wave, rolling in long after the shock has passed, if there be 
deep water close into the shore, in which case the wave will come in as a 
long and wide, but low and unbroken swell, and may do little or no damage, 
which fully explains Darwin’s case of Valparaiso, as above quoted.* In this case, 
if more than one great sea wave arrive to land, there must have been more than 
one earth wave; in fact, there will be one sea wave for every earth wave or 
shock, but the intervals between the shocks may be such, or the primary impulses 
so circumstanced, that two or more such waves may arrive at the land together, 
or so nearly coincident as to appear as one; and as there is deep water close in 
shore, and, therefore, no beach, the apparent recession of the sea, at the moment 
of the shock, will not take place; but instead, there will be a small elevation of 
the sea, or forced sea wave, close in shore, at the moment that each shock reaches 
the land, the height of which will be approximately the same as that of the earth 
wave itself, and may, in fact, become a rude measure of the amount of vertical 
movement of the earth at the crest of the earth wave. 
But further, the interval of time between two shocks, or, what is the same, 
between two forced sea waves (which we must recollect always keep company 
with the earth waves), may be such, that the forced wave of a succeeding shock 
shall coincide at the shore with the great sea wave due to a preceding one, and 
thus the forced wave be obliterated, or accumulated into the great sea wave ; and 
this may happen upon certain points of an indented shore, and not on others: or 
it may happen upon certain points of a perfectly straight shore, with deep water 
all along, and not on others, provided the geological formations at different points 
along the coast, and under the surrounding sea, differ in density and elasticity, so 
that the time of the earth wave transit is greater in one formation than in ano- 
ther ; in this case, the shock will arrive a very little later upon one part of the 
coast than upon the other, and the forced sea wave along with it, as may be 
made more evident to the eye by a geological map of earthquake cotidal lines. 
(Plate I.) 
From the principles already explained, a single earth wave or shock will, 
* Page 66. 
