Mr. Matter on the Dynamics of Earthquakes. 79 
exactly what occurred after the earthquake at Callao, in South America, in the 
year 1747, as related by Ulloa in his Voyages.* 
That the whole mass of the land over vast areas is often permanently elevated 
‘more or less, and to variable amounts at different points, during earthquakes 
agitating these same areas, is proved beyond doubt; it therefore must be held in 
view that all the above phenomena of wave motion, in both earth and sea, are 
liable to perturbations, and to become complicated, by movements of permanent 
elevation or depression in the land, general or partial, and the effects of which, 
it may be often difficult or impossible subsequently to separate; but the distinc- 
tion is ever to be held in mind between those elevating forces, which have a 
common origin with the earthquake, and which permanently affect the level of 
the disturbed country, and these impulses, the transient effects of which, acting 
at remote distances, constitute the earthquake properly so called. 
It seems probable that the earth wave, in passing through a country already 
shattered, or consisting of a variety of heterogeneous formations, and with a very 
uneven surface, may become broken or separated, in the way already explained, 
into a succession of smaller shocks or earth waves, and as the amplitude or 
length of these waves is small, while their velocity is still very great, they may 
break up the mass of the rock or ground through which they pass, by the amount 
of internal motion exceeding the elastic limits of the formation, and thus give 
rise to fissures which, in hard material, may rapidly open and close, as the suc- 
cession of partial earth waves passes through. This explains the phenomena 
recorded as happening in the great earthquake of Jamaica of 1692, where the 
fissures opened and closed, in vast numbers at a time, with such rapidity, as not 
only to swallow human beings, but even to bite them in two, when in the act of 
falling in.t 
The casting out of water, mud, &c., from such fissures, seems to be merely 
an accident due to these fluids having found their way from lakes, rivers, &c., 
into the newly formed fissures when open, and bemg squeezed out again when 
they closed, or thrown out by inertia on the transit of the wave, as already 
explained in the case of springs. 
* See Caldcleugh, Phil. Trans., Earthquake at Conception, of 1835; and for a collected account 
of the coming in of great sea waves, Woodbine Parish, in Phil. Magazine for 1836, vol. viii. page 
181, t Lyell, vol, i. p. 512. 
