156 The East Anglian Earthquake.
charged with sand at Cross Farm, have already been alluded
to in the preceding portion of the Report (pp. 76 and 77).
This action of seismic disturbances upon subterranean
waters has been observed in all great earthquakes,61 and it is
not difficult to suggest, in a general way, how such effects
may be produced. The case of a shallow surface well, like
that of St. Peter's, calls for no other explanation than that
of motion imparted from below to a mass of fluid having
freedom to move in an outward direction only. The tur-
bidity of the water temporarily produced in these two wells,
was no doubt caused by the fine particles of clay, &c,
detached by the grinding movement of the beds and carried
into the wells by the momentary increase of flow caused by
the jerk imparted by the shock.
Cross Farm.—With respect to the little streamlets which
burst forth at Cross Farm, it may be suggested that the tem-
porary squeeze to which the water-saturated beds were
subjected by the passage of the wave of compression was the
immediate cause of the water appearing at the surface, the
crack opened by the disturbance at this place affording the
easiest channel of escape. In the absence of any precise
knowledge of the underlying beds, it has been somewhat
difficult to arrive at a satisfactory decision respecting the
source of the sand brought up by these streamlets. It
appears from Prof. Bonney's report (p. 77) that not much
light is thrown upon its origin by microscopical examination;
nor could a chemical analysis be expected to give any further
information. The nearest well-boring, which is at East
Mersea, passes through the following beds62:—
51 See for instance, Mallet's ' First Report on the facts of Earthquake
Phenomena,' Brit. Assoc. Rep. 1850, p. 56 et seq.
* I am indebted to Mr. W. Whitaker, F.G.S., of H.M. Geological
Survey, for the use of some of the proof-sheets of the Survey Memoir
48 N, containing the account of the above and other sections supple-
mentary to those published in Mr. Dalton's Memoir, 48 S.W.