Mr. Mauer on the Dynamics of Earthquakes. 81 
was two feet four inches.* In this instance, it seems most probable that the 
amplitude of the earth wave was so great, that the entire cavity or basin of the 
lake was, as it were, nearly at the same instant, tilted or canted up, first at one 
side, and then at the other, by the passage of the wave beneath it, so as to dis- 
turb the level of the contained waters by a few inches, just as one would cant up 
a bowl of water at one side by the hand; insucha case, the height of the original 
terrestrial disturbance would be much less than that of the subsequent swell, or 
oscillation of the water, produced by it, so that the earth wave itself, upon land, 
might be quite imperceptible to the senses directly. 
It is even possible that, when the earth wave originates at profound depths in 
the earth’s crust, it may be propagated through masses of rock of similarly high 
elasticity to various remote regions, and either escape altogether, or be very little 
felt in closely adjacent regions, whose formations are of soft, stratified rocks, of low 
and variable elasticity, reposing upon the more elastic primary rock below ; so, also, 
the earth wave will pass with wnegual velocities, in different directions, in strati- 
tied, laminated, or pseudo-crystalline formations, such as various sands or limeston es, 
roofing slate, &c. Thus, an earthquake shock originating at or near Lisbon, 
might be felt in the older rocks of Scotland or of Wales, and yet not be observed, 
or be much less observable, in England, although it should have equally passed 
under the latter country. This appears actually to have been the case, in the 
great Lisbon earthquake.t 
So, also, the earth wave or shock propagated in all directions at once, from 
the centre of impulse, if this be situated, with formations of low elasticity at 
one side of it, and those of high elasticity at the other, may reach very distant 
regions by transit through the latter, while it may be scarcely felt in closely adja- 
cent ones situated upon the former. 
Again, if two earth waves or shocks be propagated through a region towards 
a line, where, by change of formations, partial reflection of the wave takes place, 
as already explainedj, the recurrent wave of the preceding shock, may meet the 
advancing wave of a succeeding one, and a nodal line of earth wave shall result, 
so that along one particular stripe of country, at right angles to the line of transit 
of the shock, or nearly so, the destruction shall be far greater produced by the 
accumulated wave than at any one line in advance of it or behind it, and yet there 
* Lyell, vol. i. p. 507. ¢ Phil. Trans. 1760. t Page 26. 
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