976

THE COLLIERY GUARDIAN

November 12, 1915.

coal measures, and each of them terminated by passing
through a couple of hundred feet of what was clearly
millstone grit. They would see at once, therefore, that it
was out of the question to talk about correlating the seams
met with in those bore holes with the ordinarily recognised
seams of the lower coal measures in other parts of Lanca-
shire. Any correlation which might be made would be
simply nonsense. The interesting point was that all the
seams which occurred even in the lower coal measures had
become worthless at the extreme end of the coal field.
Another fact he should like to mention was that in each
of the boreholes the coal measures showed a moderate dip
of about 12 or 15 degs., but nevertheless the horizon of the
strata was pretty nearly the same in the two borings. That
was explained by the fact that they were approximately
symmetrically situated on either side of an anticlinal fold
which ran between them and crossed the coal field. Those
borings, however, were actually of very great interest as
showing first of all the modification of the lower coal mea-
sures; secondly, the position and continuance of the anticlinal
axis ; thirdly—and this was very important—the fact that
there were permian as well as triassic rocks resting directly
on the lower coal measures. While in that part of the
coal field they knew the permian rested on the upper coal
measures, so in the interval between the Wigan district
and the Knowsley district the permian has trespassed right
across the whole thickness of the lower coal measures. He
ought, before leaving that part of his paper, to express his
appreciation of the kindness and generosity of Lord Sefton’s
agents and the colliery people concerned in allowing the
results of those very important borings to be published.

Problems of the South Lancashire Coal Field.

General Structure.—Turning to the main subject, the
general structure of the Lancashire coal field, Dr. Hickling
remarked that Sir Thomas Holland had already sufficiently
emphasised the fact that the official geological map was in
some respects inaccurate; he would still further emphasise
the fact that in addition to being inaccurate, it was very
incomplete. The map certainly had a very large amount
of information collected on it, but that information had not
been worked up and connected together in the way it inight

MANCHESTER
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Structural Map of the

South Lancashire Coal Field.

1. Millstone grit

2 Lower coal measures.

3.	Middle coal measures.

have been. What he had been doing, principally as a pre-
paration for this paper, was to complete the map, and
introduce certain amendments which were made possible
by means of later information than was contained on the
map. In that way he had redrawn the map so as to bring
out the real structure of the coal field a great deal more
clearly than appeared from the original map. Let them
consider what was the real structure. Taking the original
Geological Survey map, it would be seen that in Central
Derbyshire they had the lowest carboniferous rock, viz.,
the carboniferous limestone (brought to the surface by a
great uplift), surrounding that the Pendleside rocks, the
millstone grit, and finally, the coal measures. This con-
centric arrangement was, of course, accounted for by the
fact that the rocks in that region were lifted up into the
form of an arch, and the crest of the arch had worn away
so that the lowest rocks were exposed in the centre, and
they got a succession of higher rocks on either side. The
usual presumption was that the Pennine arch dipped away
under Cheshire ; all the rocks dipped under the great Cheshire
basin, so that the westerly limb of the Pennine arch formed
the eastern portion of the Lancashire and Cheshire coal field.
That dip continued until they got to the border of Wales,
and then the rocks began to turn up again; there was
another great uplift along the eastern margin of Wales. So
far as that was concerned, the rocks of Cheshire and South
Lancashire lay in a direct trough between the Pennine arch
and the uplift of Eastern Wales. But further than that
there was another uplift running across the middle of
Lancashire; an arch running through the Rossendale area
bringing up the millstone grits and so dividing the South
Lancashire coal field from the Burnley coal field; another
uplift along the east and west lines at right angles to the
first one which gave the rocks in that area a southerly dip
again into the middle of the Lancashire basin; then finally
further south an uplift giving the rocks a northerly dip.
Those four uplifts combined to enclose the basin-shaped
depression of Cheshire. That was the general view of the
structure of the Cheshire basin, and if at were correct, one

would expect to find that a section across that basin would
give the arrangement of rocks in the form shown. It was
generally assumed, that the Cheshire basin was a simple
trough; that the coal measures were at the surf ace on the
eastern side, and then they dipped away under the new red
sandstone deeper and deeper into the middle of the basin,
and were buried until finally they came up again in the
Ruabon coal field. Assuming that to be correct, they knew
that the dip on the eastern limb of the basin was fairly
steep, so that beyond a very short distance from the margin
of the coal field the coal measures were so deeply buried as to
be inaccessible

Limit of Concealed Coal Field.—If that were so, they
could only hope to go a short distance under the new
red rocks in working coal; within a mile or so of the
boundary the coal measures would be so deep as to be
inaccessible, and the further one went the deeper they would
become. The net result would be that the available coal
field in Lancashire and Cheshire would be limited to an area
extending a very short distance beyond the limit of the
visible coal measures; within a mile or so beyond that
boundary would be the furthest they could expect to work
into the basin. Now’ what he hoped to make out a case
for was that they might work a very much greater area
under those new red rocks. To support his proposition he
called attention to a map he had made, which brought out
more strongly the details of that part of the Lancashire
coal field with which he was more specially concerned. On
the map were distinguished the millstone grit, the lower
coal measures, and the middle coal measures divided into
four portions. The lowest limit of the middle coal measures
was taken over the whole area of the map as the Arley
mine. The first division ended wTith the Cannel, then the
second division ran from the Cannel to the Dow, or its
presumed equivalent, the third from the Dow to the Rams,
the fourth from the Rams to the Worsley Four Foot.
Finally there were the upper coal measures. He would
point out that taking the northern portion of the coal field,
the rocks in general had quite a definite east and west strike
—that is to say, the outcrops ran east and west—but it was
equally clear that the east and west strike was completely
upset along two lines. In an area starting from



4.	Upper coal measures.

5.	Permian.

6.	Trias.

Manchester, lying between two faults, the rocks were com-
pletely disturbed; they were not only shifted out of their
proper places, but also twisted round in various ways.
Instead of running east and west, the outcrops were for the
most part pulled round into a north-west and south-east
direction, more or less parallel with the boundary faults.
Once they got out of that area it was fairly plain sailing
until they came to another pair of faults, between which
there was -an exactly similar state of things, the outcrops
being all pulled into a north-west and south-east trend, so
that instead of having southerly dips in the coal they had
in general an east and west dip. That was in the Wigan
patch. Those were two of the most striking features of
the Lancashire coal field. In what might be termed the
Manchester tract, running up to Bolton, and in the Wigan
tract, the structure of the coal field was completely turned
round.

Disturbances in the Lancashire Coal Field.—Coming back
to the general map they would observe that at the eastern
edge there was a very sharp bend round almost at a right
angle; the east and west trend of the rocks was lost, and
they got a definite north and south trend. For a consider-
able distance that north and south trend went on, but just
in the region of Romiley there was a sharp twist, which had
been very largely omitted from the original map, the reason
being that there was another line of folding leading to that
twist in the boundary. Another feature he wished the
members to observe was that to the west of the Wigan line
of smash the trend of the rocks suddenly changed from east
and west to a very definite north-east and south-west trend,
parallel to an anticline running through the Croxteth inlier.

It would therefore be clearly seen that the structure taken
in detail was much more complicated than the general struc-
ture which he described at the beginning of his address.
They had on one side the Pennine uplift, which was respon-
sible for the north and south trend of the outcrops ; the Rossen-
dale uplift was responsible for the general east and west trend
of the outcrops in one region; the Knowsley, or Croxteth.
uplift brought about the north-east and south-west trend

in another region; then, as quite independent features, they
had the two great smashes at Manchester and Wigan, and
also the uplift or anticline which ran through Romiley. Going
a little further afield, to the area north-east of Congleton,
they came across another striking feature. First of all, the out-
crops of the coal bent round sharply to the north-west,
followed by the ridge of millstone grit. It came down a little
further, and then was abruptly turned round, and they had
very high dips to the north-east. The result was that they
very soon passed from the lower coal measures over the
millstone grit, and down to the Pendleside rocks. To the
south again the series was reversed — millstone grit, lower
coal measures, middle coal measures, and so on, into the
North Staffordshire coal field. In other words, there was a
powerful uplift, which brought the Pendleside rocks to the
surface, and further inspection showed that that uplift must
run in a north-west to south-east direction. Continuing the
uplift in that direction, it inevitably ran across the Cheshire
basin, and joined up with the great line of dislocation which
cut the coal field in two at Wigan. There could be no doubt
that was one continuous line of disturbance, showing itself
at Wigan in the form of a definite anticlinal fold. It was
very difficult to find a term by which to describe that dis-
turbance; there was a very serious complex series of faults,
combined with a complex series of folds, but nevertheless,
taking the structure of the Wigan tract very broadly, it
would be found that the effect of it was this. If one took a
■section across the Wigan tract it would be found that there
were boundary faults of that kind letting down the Wigan
area as a great trough; inside that trough the rocks were
folded, broadly speaking, into an arch. There were many
little folds, and a great deal of complication by minor
faultings, but that appeared to be the general structure;
it was an anticlinal fold let in. Something of it could be
seen in the form of the outcrop of the upper coal measures;
the V shape indicated on the map was due to that arch. In
the Manor tract it appeared to be much the same; the upper
coal measures came down, and then were sharply bent up.
In the same way they had an anticlinal fold which was let
down between two faults. Each of those areas represented
an anticlinal fold let in between a pair of faults.

Before going on to discuss the importance of those
structures, it would be well to fix them more clearly by
examining the general trend and relative position of the
features of the area he was dealing with. Those features
were the Rossendale anticline, the Manchester series of
smashes, the Wigan series of smashes, the Knowsley anti-
cline, the Romiley anticline. Another powerful uplift formed
the western margin of the North Staffordshire coal field; it
might be termed the Audley anticline. A north and south
uplift—the Endon anticline—formed the eastern boundary
of this field. Then the Pennine uplift had a subsidiary arch
running parallel with it along its western flank; it might
be described as the marginal anticline.

Practical Importance on Correlation.—As far as could be
made out, these were the essential structures which governed
the arrangement of the rocks in the Lancashire and Cheshire
coal field. Another little point he might refer to was this.
One of the greatest mysteries of the coal field had always
been the tract to the north of Manchester. At present there
was a large area which was a blank so far as their knowledge
of the field was concerned, and most of them were doubtless
aware that they could follow the various seams in the
western part of the field with some confidence and correlate
them with one another. The correlation of the seams in
the eastern portion of the coal field wa-s also fairly obvious,
but when they sought to link up the eastern coal field
definitely with the western coal field they were at a com-
plete loss. He was going to try to give some idea why, as
it appeared to him, that was the case. The Irwell Valley
fault, running from Manchester to Bolton, was known to
everybody; it threw down the rocks on its eastern side to
the extent of something like a thousand yards. That great
smash did not cause them any serious trouble, because they
knew it was -there, and knew just what happened. On the
other hand, what was not indicated at all on the Geological
Survey map or any other existing map of the coal field was
the fact that there clearly must be a similar great smash
running parallel with that one some few miles to the east.
A careful analysis of the map, however, made it quite
certain, in his opinion, that that fault must be there, and
that the Manchester tract was just let in between those two
great faults. The non-recognition of that great fault was
undoubtedly one source of the mystery which had always
attached to that part of the coal field. Another feature
which seemed equally inevitable was the occurrence of the
great fault cutting diagonally across the tract through the
north of Bolton. That appeared to have a downthrow to the
north, possibly of something like 500 yds.; so far as he could
see, unless the identification of the few coal seams that
were worked in that area was hopelessly wrong there seemed
to be no escape from the existence of a great line of smash
letting down the area to the north to the extent of some-
thing like 500 yds.

He was not prepared to say that was a single fault, or
that it was not possibly a complicated series of smashes, but
in effect there must be a great fault across there. Allowing
for those features, it was possible to attempt to correlate
the eastern part of the coal field with the western part, and to
draw in the outcrops of the various subdivisions of the
middle coal measures to the north-east of Manchester. Another
considerable modification was a great extension of the triassic
and permian rocks in that area, where, according to the old
map, there ought to have been coal measures at the surface.
That, as a matter of fact, was further evidence of the
occurrence of the fault he had just referred to.

On the man he produced he had traced as far as possible
the various divisions into which he had divided the coal
measures across the field. That necessarily involved the
correlation of the seams in different parts of the coal field,
and he had had to do that to the best of his abilitv. On the
whole, the correlations were fairly accurate, but he desired
to emphasise this point, that the accuracv of the map, in so
far as it showed the structure of the coal field, depended
entirely on the correlation of the seams as between one area
and another. The structure which he had brought out by
the map was just so far reliable as the correlation of the
seams was reliable, and the accuracv of anv map of the
coal field which could ever be produced would depend on the
same feature. The correlation of the coal seams was the
essential basis of the geological map of anv coal field, and
he wished to emphasise that point specially for obvious
reasons. Taking it that the structure shown by the map
was accurate, so far as it went, it was possible from the
structure of the exposed portions, to predict the structure of
the buried portion under the trias. He could not attempt to
deal with the question in any detail, but the map would
show sufficiently fairlv the most important features.

Chief Lines of Fault.—Neglecting all trivial points in