COAL UNDER SOUTH-EASTERN ENGLAND. 145
in beds older or newer than the Carboniferous Series, of which the Coal Measures
form an upper member. Dover and Harwich are the only places in South-Eastern
England at which rocks belonging to the Carboniferous Series have been found.
But while at Dover Coal Measures were pierced, at Harwich the boring ended
in beds apparently older than Coal Measures. However, in the district where
the lower beds of a series are found, the higher are more likely to be discovered
than elsewhere.
We have learned that, east of the Straits of Dover, Coal Measures have been
found on the northern flank of a ridge or plateau of older rocks. This ridge,
though having a general east and west range, is seen, where visible, to take a
more or less sinuous course, like that of an ordinary mountain-chain. The lowest
beds yet reached in South-Eastern England are (as already mentioned) the Upper
Silurians at Ware. Between Ware and the Thames at and near London only
Devonian or Old or New Red Rocks have been discovered, as already stated ;
but we have seen that we are not justified in expecting Coal Measures on the
ancient plateau but on its northern flank. Assuming that the Coal Measures
struck at Dover are thus situated, it is evident that the range of the plateau
between Dover and Ware is nearly north-westerly in direction, and that the most
probable position of any Coalfields associated with it is on the north-eastern side
of a line connecting those towns. Thus a section between Harwich and Ware
would probably disclose a state of things more or less resembling that indicated
in the diagram below, the surface rocks being removed.
But the utter want of evidence between Ware and Harwich, and the probability
that any Coal Basins existing under South-Eastern England are comparatively
small, and detached from each other, will make a series of borings necessary before
the subterranean geology of Essex and Suffolk can be clearly intelligible. Every
boring, however, will add to our knowledge, and it matters little or nothing
whether the Coal Measures themselves are pierced in the first boring or only in
the third or fourth, as it is almost as important to know where they are not as
where they are. The accidental discovery of Coal Measures at Dover, for
example, tells us nothing about the size of the Coal Basin touched, or the
directions in which it extends. It may lie mainly between Dover and Canterbury or
Dover and the Goodwin Sands, and may accordingly be either workable or almost
entirely out of reach. Nor does it show whether there is, or is not, any inversion
of the beds. In short, its interest and importance resemble that at Burford. As
the Burford boring proves the existence of a Coal Basin under Secondary rocks
many miles eastward of the Coalfields of Bristol and of the Forest of Dean, so the
Dover boring demonstrates the existence of coal under Secondary rocks about an
equal distance westward of the nearest continental Coalfields.
In selecting a site for the first experimental boring in the Eastern Counties, I
should be inclined to favour one somewhere between Ware and Harwich, but
much nearer to the latter town. Probably a spot three or four miles north-east