146 COAL UNDER SOUTH-EASTERN ENGLAND.
of Colchester would be a good place, as in that district the top of the Chalk is
within a few feet of the surface, and it is also obviously better to begin near the
place at which Lower Carboniferous rocks are known to exist than where beds of
some other series are more likely to occur, as in Western Essex. An additional
presumption in favour of this spot seems to me to be furnished by its position
with reference to the area within which structural damage was done by the Essex
earthquake of April, 1884. If a straight line be drawn, having a north-west and
south-east direction, parallel with the general course of the Colne between
Colchester and the sea, and about two miles east of the river, this line gives us
the eastern limit of damage. The western limit might be similarly shown by
a line parallel with the first and connecting Coggeshall with Tillingham, south of
the Blackwater, the northern boundary being another line between Coggeshall
and Colchester. Of course there are a few outlying places at which some damage
was done, but at least nineteen-twentieths of it took place within the area
described, as may be seen on the map given by Professor Meldola and Mr. White
in their report on this earthquake.3 Now it seems to me that the most probable
explanation of the restriction of the damage to so compact and limited a district is
to suppose that the ancient subterranean ridge or plateau is unusually near the
surface there, while it speedily becomes deeper towards the north-west of Colchester.
And as we may expect Coal Measures, not on the ancient ridge, but here and
there on its more northerly flank, it seems best to begin operations a little north-
east of the area of earthquake-damage.
P.S.—The result of the Culford boring (learned since the above Report was
sent in) does not seem to me to make any modification in what I have written
desirable.
II.—REPORT BY W. WHITAKER, B.A., F.R.S., F.G.S.,
ASSOC. INST. C.E. (Hon. Mem. Essex Field Club).
The question of the probability of an uprise of Older Rocks underground in
the South-East of England was first started, as a matter of reasoning, a good
many years ago. The effect of such an underground uprise would be to interrupt
the continuity of many of the beds below the Chalk, by bringing much older
formations nearer to the surface than they would be if the Upper Cretaceous
beds were duly underlain by Lower Cretaceous, Jurassic, etc., as at the outcrops
on the north, west, and south.
The line of reasoning was as follows : It was suggested that the uprise seen
in parts of South Wales and in the Bristol district, with a general direction more
or less west and east, was likely to be connected underground with the other like
uprise through Northern France and the neighbouring part of Belgium, although
that connection was hidden at the surface by a covering of Tertiary, Cretaceous,
etc., rocks. As a consequence of this hidden uprise the continuity of the Jurassic
and Triassic rocks underground would be imperfect, so that in many places the
Cretaceous beds would be found to rest directly on much older rocks, whilst in
other places these two might be separated by no very great thickness of Jurassic
rocks.
It was argued, too, that amongst the older rocks thus brought nearer to the
surface Coal Measures were likely to occur, probably in a set of separate masses,
as in South Wales and round Bristol.
3 "Report on the East Anglian Earthquake of April 22nd, 1884." ("Essex Field Club
Special Memoirs," vol. i.) London: Macmillan & Co., and Essex Field Club. Buckhurst
Hill.