142 SUBTERRANEAN GEOLOGY OF SOUTH-EASTERN ENGLAND.
of reaching the Palaeozoic rocks after piercing through the fewest
formations of Secondary age, this locality seemed the best that could
be chosen for the experimental Sub-Wealden boring, which was
actually carried on during the years 1872-5. But though the deepest
yet made in south-eastern England—attaining a depth of 1905 feet
—it not only failed to penetrate to Palaeozoic rocks, but even to
reach the base of the Oolites, in whose uppermost beds it was begun.
Indeed, there is nothing in the arrangement of the Secondary and
Tertiary rocks of S.E. England to suggest any great irregularity
in the Palaeozoic floor on which they rest. Folds exist such as that
of the Weald, or the much sharper one traversing the Isles of Wight
and Purbeck, but nowhere east of a straight line drawn from Hull to
the Isle of Portland do we see on the geological map patches of
Palaeozoic rocks surrounded by strata of Secondary age, a sight
extremely common west of that line. We have yet therefore to
ascertain what grounds exist to justify the theoretical view put
forward more than thirty years ago, that Palaeozoic rocks might be
reached at a moderate depth under certain parts of S. E. England ;
and to compare these conclusions with the results of various borings
that have since been made, chiefly in the neighbourhood of London.
On May 30th 1855, a paper was read before the Geological
Society, by the late Mr. Godwin Austen, "On the possible extension
of the Coal-measures beneath the S.E. part of England." ("Quarterly
Journal of the Geological Society," vol. xii. page 38). The author
drew attention to the fact that if we cross the Channel to Belgium,
we find that from the valley of the Ruhr to that of the Scheldt near
Valenciennes, there extends for 170 miles from east to west a
continuous series of productive Coal-measures, which lie on the
northern edge of a ridge consisting of still older rocks. From
Valenciennes westward (he remarked) the Coal-measures are covered
by later formations, and take a direction by Douay, Bethune, and
St. Omer to Calais, having been met with on boring for water at the
last-named place. This ridge with its coal-basins, doubtless existed
beneath the Secondary rocks of S.E. England.
A glance at a geological map of Belgium shows that on or close
to this belt of Coal-measures the towns of Aix-la-Chapelle, Liege,
Namur, and Charleroi are situated, outlying patches appearing W.
of Charleroi, in the neighbourhood of Valenciennes. South of
this belt of Coal-measures the country is composed, for a breadth
of many miles, of Palaeozoic rocks mainly of Lower Carboniferous