1197

June 23, 1916.

_______________________________________________

Some Effects of Earth Movement on the Coal Measures

of the Sheffield District, etc.—Part 11.*

By Prof. W. G. FEARNSIDES, M.A.

(Continued from page 1090.J

Pre-Permian Contours of the Barnsley Bed.

The heights, above the Barnsley bed, of -the surface
upon which the permian rocks were deposited have
been deducted by subtraction. For this two kinds of
evidence were available, namely :—

(1)	The direct evidence provided by such shafts and
boreholes as pierce both the base of the permian and the
Barnsley bed. From such records; by the subtraction
of the number taken as the depth to the base of the
permian from that of the depth to the Barnsley bed, a
new series of numbers is obtained, which, if distributed
with sufficient regularity, may serve as spot-levels for
the running of contours in the manner previously
described.

(2)	The indirect evidence obtained by the study of the
contours already plotted, bearing in mind that

Fig. 3.—Approximate Underground Contours of the Pre-Permian
Surface of the Coal Measures and of the Barnsley Bed.

(The interval between successive contours is 100 yards.)

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geometrical property of contours by which, if two series
of such lines, both drawn with the same arbitrary but
convenient interval between their successive members,
should intercross, the difference of height between the
two sets at a pair of opposite corners of each quadri-
lateral of the net formed by their crossing must always
be the same, and the diagonal (not necessarily a straight
line) joining these two corners must represent a contour
of equal differences. By joining, then, the pairs of
opposite corners of all the various spaces of the net
formed by the intersection of the pre-permian and the
Barnsley surface contours, and “ sweetening ” the
angularity of the lines, a series of contours recording
the variations of the depth of the Barnsley bed below the
permian within the area over which the permian rocks
occur is obtained. Fig. 3, showing the contours for (1)
the base of the permian, and (2) the Barnsley bed, was
prepared by tracing directly the contours as plotted on
the half-inch map, and subsequent reduction by
photography.

For fig. 4 the tracing used for fig. 3 was worked upon,
and diagonals showing the lines of constant difference
were drawn in across the spaces of the net, half and
quarter-way contours being freely sketched in order to
show the intermediate points of intersection wherever
there was a doubt, and where the sweetening of an
awkward bend of the diagonal in the midst of a
quadrilateral, the sides of which are more than usually
out of straight, was required. The new curves also were
slightly adjusted, where necessary, into complete
agreement with the direct evidence afforded by all
available boreholes, to form the 'eastern half of fig. 4.
The direct measurements made use of in controlling the
contours of this diagram are, in order of increasing
differences, as follow :—

* From a paper read before the Midland Institute of
Mining, Civil, and Mechanical Engineers.

THE COLLIERY GUARDIAN.

________________________________

Feet.

390
600*
605*

765

873

904

972

1,038

1,085

1,085

1,158

1,218
1,285*
1,306
1,317*

1,347 J

Feet.

1,361
1,389
1,394
1,396
1,432
1,378*
1,534
1,585
1,589
1,593
1,654
1,694
2,057 .
2,249*

2,276
2,369*

Frys ton ....

Sutton .....

Ba ribo rough

Whitwell ....

Southgate ...

Kirkby ....

Selby .......

Sherwood

Creswell ....

Rufford .....

Mansfield ....

Thorne ......

Clipstone

Shireoaks ....

Hatfield Main	......

Bentley ....

...........	Warsop Main .......

...........
Pleasley ............

..........

.......	La ng with .

Haxey (South Car) ...

Shirebrook .........

Cantley ............

Man ton ............

.........	...........

...........

...........

............
............

Welbeck .............

Steetley ............

Brodsworth Main ...

Bullcroft Main ....

......

Askern Main .........

..........	Rossington Main ....

Wallingwells ......
Maltby Main ......

Yorkshire Main ....

* Denotes approximations.

To the west of the permian outcrop, the completion of
the con toons showing the

depth of the Barnsley coal
below the base of the per-
mian is founded on more
theoretical evidence, which
depends upon an exterpola-
tion of supposed contours
for the base of the permian
over the area from which
all trace of permian rocks
in situ has long been re-
moved. Nevertheless, be-
cause the geometry of the
known surface at the base of
the permian has been
proved to be simple, and its

of full dip (that is,

contours are spaced so regu-
larly over the whole of the
area shown on the map,
and because the geometry
of the Barnsley bed in the
exposed coal field has been
so completely proved by
mining, the writer has
thought well to undertake
the exterpolation and to put
. on record the results. The
method of the exterpolation
for the contours of the base
of the permian beyond its
outcrop was as follows:—
On the tracing from which
fig. 3 was prepared, lines
were drawn along the direction
at right angles to the contours of the permian) at such
intervals as to cut the area into squares, and these dip-
lines were continued out over the exposed coal field.
Along these lines distances were marked off which to the
eye seemed not out of sympathy with the average
distances within the permian ground, and through the
points so found hypothetical contours for lines at
successive hundreds of yards over the country as far
westward as the Barnsley bed outcrop were drawn in.
These sketch contours were then treated as if they had
been obtained by more direct observation, and through
the net of their intersections with the proved contours
for the coal-seam diagonals were drawn as before, and
traced off to complete the diagram (fig. 4) in continuity
with the lines of equal differences east of the permian
outcrop. As already shown (see fig. 3), the courses of
all contours of the pre-permian surface between that of
4- 200 yds. in the outliers west of Mansfield and that of
— 800 yds. along the lower course of the Trent, are

fairly well known. By exterpolation it would seem that
if similar slopes are continued westward,-the base of the

permian would, be- carried to + 400 yds. (about Wake-
field, to + 500 yds. at Barnsley, and to + 600 yds. in the
neighbourhood of Sheffield, where is the highest exter-

pointed contour which the area dealt with on the map
•requires. With respect to the shapes which these
contours of equal differences take, a glance at fig. 3 will

convey more information than a long description. One
feature which the eye notices immediately is that the
alignment of centres round which the lines of greatest
differences circle is along a north-western and south-
eastern line through Leeds and Worksop. Of the two
well-marked widely open basin structures the one has
its centre at Brierley Common, about midway between
South Kirkby and Grimethorpe pits; the other, which is
situate south of the Don fault disturbance, has its
centre at Brumley, not far from Maltby. In the central
areas of each of these basins the thickness of coal
measures which remained above the Barnsley bed
when the "permian rocks were deposited, over several
scores of square miles, must have exceeded 700 yds.,
and in the Maltby basin over a considerable area the
thickness that actually remains is more than 800 yds.
South of the Yorkshire boundary the cover of coal
pleasures above the Top Hard coal is generally thinner,
and nowhere is there any evidence that it attains 600 yds.
Within the parts of the area which belong to Derbyshire
and Nottinghamshire it would appear that distribution
of the contours of equal thicknesses of measures is
entirely dependent on the disposition of the north-west
trending ridges of Mansfield and Brimington, Barl-
borough Ridgway and Norton, and Kivoton Park, the
courses of which the writer has already discussed.
There is some evidence that at Steetley and Man ton,
and at Welbeck, localities at each of which more than
500 yds. of coal measures have been proved, the pits are
situate not far from the centre-lines of the troughs which
come between these anticlinal disturbances.

Concerning individual contours, the situation of a
zero-line, which is the line in which the base of the
permian meets and cuts off the Barnsley bed, may first

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Fig. 4.—Pre-Permian Contours of the Barnsley Bed
(The interval between successive contours is 100 yards).

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be noted. Direct evidence for the junction is nowhere
seen, but in the south the outcrop of the base of the
permian crosses the line which has been taken as the
outcrop of the Top Hard coal beneath the permian out-
lier about a mile east of Tibshelf; and it seems probable
that, before the present cycle of denudation, the permian
must have rested on measures older than the Top Hard
coal a mile or two further north near Hardstoft, and also
on the west side of the Williamthorpe syncline, as well
as for some distance along the crest of the B riming ton
anticline. In the district from Elmsail northwards the
permian begins the transgression which carries it across
all members of the middle and lower coal measures and
the millstone grit series, and near Richmond brings it
to rest directly on the carboniferous limestone. The place
of the actual transgression of the outcrop of the Warren
House coal by permian rocks is obscured by the Kippax
fault, but lies to the south of and cannot be far from the
Ledstone Luck pit. Beneath the permian the line got by
intersections of the permian base and the Barnsley bed