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pression though the solid crust of the earth, produced at any 
distant points, by any original sufficient impulse, such as the 
sudden bending, by elevation or depression, or the rupture of 
a portion of the earth’s crust. 
From this single principle, viz., that the true earthquake- 
shock consists simply in the transit through the solid crust of 
the earth of a wave of elastic compression, which the author 
believes to be now, by him, for the first time, enunciated, 
he proceeds to develope and account for, in detail, all the 
more important recorded phenomena of earthquakes, as well 
as many of the more perplexing secondary phenomena. 
The original impulse, or origin of an earthquake, may be 
either under the sea, or on land, at a distance from the sea. 
In the former case, at the moment of originating the impulse, 
whether by bending or fracture, several distinct sets of waves 
set out from the same points, and at the same moment of 
time, but they move with very different velocities, 
The wave of elastic compression, or great earth-wave of 
the author, makes its transit through the solid crust, outwards, 
in all directions, from the point or points of impulse, and 
moving at a speed proportionate to the specific elasticity and 
density of the formations through which it passes. This, 
the author shews, may be as much as 11,000 feet per second. 
This wave constitutes a real undulation of the surface through 
which it is passing, and may be also (if there is fracture at 
the origin) heard as a sound-wave in the solid, moving at 
the same rate. A sound-wave also travels through the water 
of the sea, and, moving more slowly than in the solid, is heard 
upon land after the shock has passed. Lastly, a rolling wave 
of translation, or great sea-wave of the author, is formed by 
the movement of the bottom, directly above the originating 
disturbance. This sea-wave, though setting out at the same 
moment as the shock or earth-wave, is rapidly outstripped by 
the latter—because its motion is dependent upon its own form 
and magnitude, and upon the depth of the sea upon and 
