170 The East Anglian Earthquake.
expression " fault line of the Colne Valley," made use of by Mr.
Kinahan (p. 91), must only be taken in a general sense as
referring to the break in the continuity of a formation caused
by the excavation of a river valley through it. The village
stands partly on alluvium, partly on London Clay, and partly
on drift-sand and gravel, and it is possible that the damage
was increased by junctional effects, as well as by the mar-
ginal situation of the buildings along the quay. But after
allowing for these effects the damage still appeared to us to
be greater than would have been expected from the situation
of the village with respect to the centre of maximum action,
and this, together with the circumstance that the damage
towards the N.E. ended abruptly at Wivenhoe, led to the
conclusion already expressed (p. 92), that the seismic wave
may have undergone a large amount of reflexion at this
place. In the absence of distinct evidence we cannot there-
fore connect the great destruction at Wivenhoe with any
special geological conditions, but it may be suggested that
the effects were purely mechanical, depending possibly upon
the circumstance that the wave emerged along this valley at
a critical angle with respect to the bounding surfaces of land
and water.75
In connection with the present discussion of the damage
at Wivenhoe, the apparent protection of some houses by the
railway-cutting (see p. 86) may be here considered. The
action of a trench in arresting earth vibrations has been
observed by Milne and others. In some experiments con-
ducted by Major Palmer, R.B.,76 it was found that in a
trench 8 ft. long and 3 ft. wide, dug in a coarse pebble-gravel
400 yards from a line of railway, a vessel of mercury was
not thrown into vibration by the passage of a heavy goods
train when the depth of the trench had reached 31/2 ft. With
respect to earthquake movement, Milne77 has found that
cuttings " are more or less effective in interrupting a dis-
turbance." It is possible that in the present case the
75 Mr. Whitaker has called my attention to the fact that at East
Mersea the chalk was reached at a depth of only 115 feet (see p. 157),
whilst at Colchester it is 144 feet from the surface. From the general