156 SUBTERRANEAN GEOLOGY OF SOUTH-EASTERN ENGLAND.
looked for south of the Thames, whether covered only by Cretaceous
strata or by Triassic beds as well. Thus, as regards the triangular
space included between straight lines connecting Richmond and
Chatham on the south, with Ware on the north, Coal-measures would
seem only likely to be found, if anywhere, along the line between
Richmond and Chatham. South of this line the Jurassic rocks
evidently thicken rapidly towards the borders of Sussex, as the results
of the Chatham and Sub-Wealden borings have so amply shown.
But it appears to me, looking simply at the scanty available evidence
(the natural inferences from which might be seriously modified by the
results of a single additional boring), that we are more entitled to
expect the preservation of coal-basins north-east of Ware than south
of Richmond and Chatham; along a line ranging from Ware through
Bishop Stortford, Braintree, and Colchester, or thereabouts. For as
we have seen, both on the continent and in Western England, coal-
basins are found north and not south of the ridge of older rocks, of
which here the Upper Silurian of Ware would seem to be the crest,
or at least, the nearest approach to it yet proved. Possibly a single
boring about midway between Ware and Harwich, might give infor-
mation as to the position of subterranean coal-measures hitherto
unattainable. And apart from any question of speculative proba-
bility or the reverse, a boring in this quarter is specially desirable in
consequence of the great distance between Harwich and the deep
borings nearer London. But we learn both from the Franco-
Belgian coal-producing districts and from South-western England
that any coalfields in this intermediate country will be found to
exist as isolated basins of no great size, which might easily be missed
in a single boring planned with much more knowledge than is at present
available.
But while two or three borings might give purely geological
information of the highest interest and value, and might possibly
demonstrate the existence of a coal-basin of considerable size beneath
the Cretaceous rocks of Essex or elsewhere, it by no means follows
that it would pay to sink to and work the coal thus found unless the
cost of obtaining it from our present coalfields had become very
much greater than it now is. And I trust the time is far distant
when it will be thought desirable to make deep borings in Essex or
Kent, simply on the economical ground that our old coal supplies
are failing, and it is therefore of the utmost importance that new ones
should be opened out. At the same time I should be very glad to