The Earthquake in Relation to Geological Structure. 167
vibrating freely till some margin is reached where the shock
may make itself felt for the reasons given, although but
slight effects or none at all may be observed at intermediate
stations. The resistance to horizontal movement which leads
to the apparent exaggeration of the effect along free margins
may be regarded as analogous to the resistance to vertical
motion, which prevents the vibrations from producing any
effect at or near the epicentrum till the surface-particles
partake of the movement.
An examination into the records of former earthquakes in
various parts of the world has convinced us that the tendency
of the shock to make itself felt along sea-coasts and river-
margins is a character of earthquake-movement which may
fairly be ascribed to the foregoing conditions, although, with
the exception of Milne,70 our most indefatigable worker in
seismology, no writer appears to have laid much stress upon
this phase of the subject. As an illustration Milne refers to
the earthquake of 1857, which affected the Alps from Geneva
to the E.N.E. On reaching the edge of the deep glen between
Zermatt and Visp the wave-movement caused large masses
to be detached all along the margin, "and heavy falls of rock
encumbered the western side of the valley." With reference
to the Japanese earthquake of February 22nd, 1880, Milne
states that in Yokohama, "out upon the flat ground in the
settlement at a distance from the bluff, the destruction of
chimneys was comparatively small, whilst at the foot of the
bluff and upon the top of it there were but few buildings
which had escaped. From the manner in which all the
grave-stones lying near to the edge of steep declivities had
been moved, whilst those which were further back were not
disturbed, it seemed that it was near to the edge of the bluffs
that the movement had been the most violent."
Without burdening this report with too many illustrations,
we may refer to the memoir on the earthquakes of 1880 in
the Island of Luzon, by Don Jose Centeno Y Garcia,71 in
which the author makes the following statement:—
70 Trans. Seism. Soc. Japan. Vol. i., part. 2, p. 77.
71 Trans. Seism. Soe. Japan. Vol. v., p. 55.