Mr. Matuer on the Dynamics of Earthquakes. 95 
But again, as the height or elevation of the great earth wave is a function of 
the depth of the solid elastic crust which has been put in motion, future accurate 
observations of this coefficient will enable us to determine the actual depth from 
which earthquake dislocation has come, and to which it laterally extends. 
This would throw light upon the otherwise inexplicable facts observed at 
various periods, namely, of earthquake shocks being felt at a given depth, and 
not at the surface of the same place, and wice versd. Thus, in 1802, the miners 
in the deep silver mine of Marienberg, in the Hartz, were frightened from their 
work by a shock which was not perceived by those at the surface; while, in 
1823, the surface shocks felt at Fahlun, in Sweden, were not perceptible under 
ground. Whatever be the depth of the plate, or band of rock, originally dis- 
turbed or constrained, the same will be the depth to which the lateral transit 
of the earth wave will be principally confined. Hence, if the original impulse 
is deep, the shock will be, in some degree, limited to the same plane of level, — 
if superficial, the shock will not extend in depth. 
Again, the amplitude of the wave bears a relation to the diameter or extent 
of the area of original disturbance, or centre of impulse; and hence, observa- 
tions as to this dimension of the earth wave will give some approximate informa- 
tion as to the area of original disturbance, though, perhaps, buried profoundly in 
the ocean. 
Other, not less interesting, but less immediate, deductions will occur, in which 
this application of physics and mathematics to geology may explain some of the 
most obscure and perplexing marks of former movements in the earth’s crust 
that we now behold. Who can explain at present the straight line course, held 
on for miles by faults and dykes, often cutting equally through every formation 
they cross at the surface ?. Who can give a plausible solution of the fissures which 
traverse the coarse conglomerate of the south of Ireland, cleaving with a perfect 
plane, like a sword-cut, through the great quartz pebbles, and through the 
softer cement, alike regardless of changes of texture or of hardness in the mass ? 
May not these, as well as many of the greater fissures now constituting 
mineral veins, be the evidences of dislocation produced by the passage, from 
enormous depths, of elastic waves, whose times of transit have been suddenly 
altered, by passing from one formation to another, at depths altogether below 
our observation or means of present knowledge, lines of broken unison, in 
