The Earthquake in relation to Geological Structure. 183
elasticity of the harder rocks which dip under the newer
formations of East Anglia.
Miscellaneous Geological Observations.
In the absence of any reliable method of determining the
depth of the origin of the present disturbance, and in view of
the necessarily speculative character of the explanations of
earthquakes in general, it has not been deemed advisable to
advance any distinct views with reference to the origin of the
present shock. That the disturbance had no immediate
connection with plutonic agencies appears probable from the
remoteness of volcanic centres.87 The district shaken is not
marked by any great phenomena of upheaval, but the
evidence, as far as it has been read, points to a slow rate of
depression.88 The most feasible explanation, in so far as it is
safe to hazard any explanation at all, appears to be that of
the sudden rupture of deep-seated rocks under a state of strain,
the snap and shock accompanying such a fracture being quite
competent to produce the effects observed.89 The precise
formation in which this rupture may have occurred cannot
even be conjectured; but the great extent of the shock on
the one hand, and on the other the absence of any perceptible
change of surface-level, appears to point to a tolerably deep-
seated origin.90
87 As a result of the discussion of 387 earthquakes in North Japan,
Milne concludes that the seismic activity in the immediate neighbour-
hood of active or recent volcanoes is but small, or, in other words, that
the seismic and volcanic activity are not directly related (Trans. Seism.
Soc. Japan, vol. vii., part 2, pp. 76—77).
88 " Subsidence in Bast Essex," by W. H. Dalton., F.G.S. Geol. Mag.,
vol. iii., 1876, pp. 491—493.
89 See Milne's Report on the Japanese Earthquake of February 22nd,
1880. Trans. Seism. Soc. Japan, vol. i., part 2, p. 59.
90 It is much to be regretted that we have had no opportunity of
ascertaining whether any change of level is indicated by the Ordnance
bench-marks, but this measurement may be here commended to the
attention of the Ordnance Survey Office. In a tract of country presenting
such an indented coast-line as East Essex, and watched so constantly
by an experienced maritime population of fishermen, yachtsmen, &c, it
is certain, as already mentioned on p. 172, that any slight change of level
would have been detected. Our closest inquiries have, however, only