666

THE COLLIERY GUARDIAN.

October 6, 1916.

have been largely caused by contraction of the marls
under pressure and by loss of moisture.”

Prof. Fearnsides has directed attention to a research
by Sorby upon the contraction of clay sediment due to
loss of water; and this may help us to clear up some of
the difficulties referred to. If the coal measure clays
have lost something like five-sixths of the original thick-
ness they possessed as mud or slime, as Sorby’s quanti-
tative experiments seem to indicate, is it not possible
that the discordance we are discussing between the
middle and upper coal measures is due, in part at all
events, to differential contraction and consequent local
sagging during the extremely slow squeezing out of the
water by the pressure of overlying sediment? We must
remember that the middle coal measures consist essen-
tially of clays, and that over a large part of the Mid-
lands they were deposited on a very uneven floor, and
that to start with they were therefore of very variable
thickness. It is easy to see, also, that an arenaceous
fringe of sediment where the measures abut against a
rise in the floor would suffer far less vertical contraction
from this cause than . the clay, because of the very
diminished ” surface energy ” of the constituent sand
particles, and that this would have the effect of accen-
tuating the dip due to the sag.

It is to be noted that Scott’s observations and the
bulk of his section referred to the central parts of the
coal field, while Clarke deals primarily with the district
just north of Madeley and along the south-eastern
fringe of the ” Limestone fault,” which may prove to
be, in its early stages at all events, a pre-coal measure
ridge of limestone.

It is quite possible that portions of the undulating
surface of the middle coal measures suffered local
erosion, which, however, need not imply folding of the
beds with prolonged subaerial denudation; for it seems
likely that such local erosion was subaqueous, producing
a non-sequence similar in character (and origin perhaps)
to the relatively small stratigraphical breaks which have
been recognised recently in the Jurassic strata in the
West of England and elsewhere. Thus, in North Staf-
fordshire, where the Midland coal basin is deepest, no
break between the upper and middle measures
exists; but approaching the southern margin of the
basin, to the south of the South Staffordshire coal field,
where the middle coal measures are rapidly thinning,
there are, if Mr. Kay’s observations are correct, signs
of a non-sequence or local nonconformity. The same is
true, but on a larger scale, in the Symon fault of the
Coalbrookdale coal field, and is to be explained, if the
above reasons are valid, by the rapid variation in thick-
ness of the middle measures, due to the irregular floor
upon which they rest, to the consequent sagging of the
beds, and also to local subaqueous erosion. Further, such
partial unconformities or n on-sequences would generally
indicate the proximity of that marginal fringe where the
upper features overlap the middle, and rest on pre-coal
measure strata.

The middle and upper coal measures of the Midlands
record general but intermittent subsidence, with a con-
siderable pause at the end of middle coal measure time,
followed by a much more general depression, as shown
by the extended and overlapping sheet of upper coal
measures. But there is no convincing evidence that
regional elevation or great orogenic movements occurred
until after the upper coal measures were laid down.

The floor upon which the middle coal measures were
deposited along the southern fringe of the Midland coal
fields was a sinking and already folded and denuded
floor, and it is to be expected, therefore, that these
measures rest in submerged gulfs and estuaries, which
would mean that some, at any rate, of the several coal
basins were originally isolated, wholly or in part, and
their separation is not to be interpreted as due to folding
and subsequent denudation.

Dr. Newell Arber has argued that the middle coal
measures of Coalbrookdale, the Forest of Wyre, and the
Clee Hills were deposited in three separate basins, which
as regards the sweet coal or productive measures were
never continuous. On the other hand, just as it is certain
that the productive measures on either side of the South
Pennines were originally continuous, so it is probable
that as we go northward from this southern fringe the
productive measures spread out into more extensive
sheets.

Without wishing dogmatically to assert that the condi-
tions were exactly just as outlined, the facts so far as
known are capable of the above interpretation, which is
more consonant with the results obtained by workers
among the coal measures of the Midlands generally than
that which has been in vogue since Clarke’s paper on the
Symon fault was published.

The folding and faulting impressed upon the measures
after their deposition, as determining the position and
structure of exposed and concealed coal fields alike, are
obviously of prime importance; but involved in these
movements are those of pre-coal measure time. So com-
plex and confused are these combined disturbances that
our main hope of grasping their salient features and of
applying the knowledge to further the development of
new mineral ground is to study more closely the tectonics
of our already-worked coal fields and their immediate
borders.

As an example of such intensive geological work,
reference may be made to the detailed plotting by Mr.
Wickham King of the thick coal of South Staffordshire
on the 6-inch maps. For more than twenty years he has
been engaged in collecting and tabulating an immense
number of levels and other data from colliery officials,
and from old and sometimes half-forgotten borings; and
he has now produced a contoured map and a model to
the same scale, showing in groat detail the folds and
faults in the thick coal. The data obtained in South
Staffordshire also enable us to determine, at some places
exactly, at others approximately, the shape of the pro-
coal measure floor and the outcrops of its constituent
fwmations; and to disentangle, in part, the pre- and

post-coal measure movements. Thus we get addi-
tional evidence to show that before middle coal measure
time, denuded folds with a north-west or Charnian
trend, and other folds with a north-east or Caledonian
trend prevailed. The post-carboniferous and pre-permian
movements emphasised and enlarged some of these folds.
As already remarked, a matter of great practical impor-
tance is as to how far these pre-coal measure folds inter-
fered with the continuity of deposition of the productive
series, with, for example, the original extension of the
thick coal of South Staffordshire. Since Jukes Browne’s
time it has been known that the thick coal group as a
whole thins, and the coal itself deteriorates, southward
towards the Clent and Lickey Hills. It is the discon-
tinuity and local deterioration in an east and -west direc-
tion, beyond the boundary faults, due to pre-coal measure
flexures, and irrespective of post-carboniferous move-
ment, that have been emphasised in the foregoing
remarks.

The powerful disturbances of post-carboniferous and
pre-permian age, which have affected all our coal fields,
have recently been ably discussed by Prof. Stainier, the
Belgian geologist; while the lucid account by Dr. Strahan
in his presidential address in 1904 and "his recently
summarised views in a lecture to the Royal Institution
will be in the minds of all geologists.

It is perhaps not generally realised what a great part
the two dominant pre-carboniferous systems of folding
played in determining the trend of the post-carboniferous
flexures. In the South Pennines, in the Apedale dis-
turbance of North Staffordshire, and in the Malverns we
have nearly north and south folds due to a great easterly
thrust ; but elsewhere in the Midlands and the north the
movements were taken up, to the west of these north and
south lines by the Caledonian folds, and to the east by
the Charnian flexures. It is very instructive to watch
in the centre of the South Staffordshire coal field the old
Charnian fold of silurian rocks that make up Dudley
Castle Hill, the Wren’s Nest, and Sedgley Hill
struggling, as it were, against the newer post-carboni-
ferous easterly squeeze, which has impressed a north and
south strike upon each of the domes, arranging them en
echelon from north-west to south-east, and incidentally
permitting the great laccolitic intrusion of Rowley Regis".

It will be found, however, that the vast majority of
the folds and faults in the Midland and northern coal
fields are not along what may be called strict hercynian
lines—that is, north to south and east to west—but along
the locally older Caledonian and Charnian directions. It
was as if the great north and south flexures of the
Southern Pennines and Malverns, and the east and west
Armorican folds of the South of England, to a large
extent exhausted the mighty attack of the hercynian
movements coming from the south and east of Europe;
while smaller intervening and relatively sheltered areas
were allowed to yield alon g their old north-west and
north-east lines.

Need for Systematic Survey by Deep Borings.

After all, when we turn our attention to the possible
extension of the coal measures under the newer strata of
south-cen&ral England, the geological data at our disposal
are lamentably and surprisingly few. Notwithstanding
our eagerness to unravel the difficulties, and so to open
up new fields for mining activity, very little positive
progress has been made in the last twenty years. Of late
a few deep borings have been sunk : one near High
Wycombe, after piercing the mesozoic cover, ended in
Ludlow rocks; another at Bateford in Gloucestershire,
15 miles north of the well-known Burford boring, struck
what are regarded as upper coal measures, also resting
on silurian rocks.

At the present time it seems specially fitting to call
attention to our haphazard method of grappling with
this great economic question. Are we to go on indefi-
nitely pursuing what is almost “ wild-cat ” boring, to use
the petroleum miner’s expressive slang? Or shall we
boldly face the fact that systematic exploration is
demanded; and that this pioneer work is a national
obligation, the expense of which should be a national
charge ?

At the meeting of the Organising Committee of
Section C, already referred to, a recommendation was for-
warded to the council in the following terms :—“ The
council of the British Association for the Advance-
ment of Science recommends that the site, depth, and
diameter of every borehole in the British Isles, exceed-
ing 500 ft. in depth, be compulsorily notified and regis-
tered in a Government office. That all such boreholes
be open to Government inspection during their progress.
That, copies of the journals and other information
relating to the strata penetrated by the boring be filed
in a Government office under the same restrictions as
those relating to plans of abandoned mines.”

Not only this, but the Government should undertake
the sinking of deep.borings at selected points. This is
no new idea. In his presidential address to the Geolo-
gical Society of London in 1912, Prof. Watts pleaded
most forcibly the vital importance of a State-aided
underground survey of the area referred to above. The
work is too vast for individual effort, or even for a
private company to undertake. It is not suggested that
deep borings should be sunk with the express purpose of
finding coal. What is wanted is a systematic survey by
borings at such spots as are likely to throw light upon
the structural framework of the palaeozoic floor and the
thickness of its cover.

Of course, there are difficulties in the way of such a
scheme. There is the expense. But in view of the
enormous economic possibilities of the work, and remem-
bering that it is now possible to sink a boring to a depth
of, say, 1,200 ft., and to bring up 18 in. cores at a cost
less than £2,000, it cannot be reasonably argued that the
expense is beyond the nation’s power to bear. A levy
of |d. a ton on the coal output of the United Kingdom
for a single year would yield something like £300,000,
a capital sum that would provide in perpetuity an addi-
tional yearly grant to the Geological Survey of £15,000,

which would suffice not only to carry on this work, but
would enable the Survey to extend its functions in the
other directions I have indicated.

As to legal obstacles and vested mineral rights, if the
country could be convinced that this work is urgently
needed on national grounds, all scruples and doubts, so
agitating to the official mind, would speedily vanish.

Chemical ajid Microscopical Investigation of Coal Seams.

The recovery of by-products in the coking of coal,
which up to the beginning of the war was almost exclu-
sively undertaken by the Germans, is likely in the future
to become an important British industry. This will
ultimately demand a thorough knowledge of the micro-
scopic and chemical structure of all the important coking
seams in our coal fields.

Remembering how varied both in microscopical struc-
ture and chemical composition the individual laminae of
many of the thick coal seams are, it will readily appear
how important such a detailed investigation may
become, having regard to the great variety of these
by-products and their industrial application. Moreover,
thin seams, hitherto discarded, may pay to be worked,
as may also an enormous amount of small coal, esti-
mated at from 10 to 20 per cent, of the total output,
which up to the present has been wasted.

FOLDING SAFETY GATE FOR
CAGES.*

The safety gate shown in the figures is used on all
cages at the Esperanza and Pilares shafts of the Monte
zuma Copper Company’s mine at Pilares de Nacozari,
Sonora, Mexico. It consists of few parts, and is cf
extremely simple design, and accomplishes the purpose
of a cage gate, yet has the advantage of folding back
against the sides of the cage when supplies and materials
are being loaded.

The cages at Pilares are of the standard all-steel
design, and while employed to some extent for raising
ore in cars, they are used principally for the transpor-
tation of men and supplies required in the mine. The
cages have a single deck just large enough for one
steel mine car of the usual 20 in. gauge, end dumping
type. The back and two sides of the cages arc covered
by steel plates bolted to the frame extending above the
cage floor to a height of 44 ft.

Fig 1 Fron+ ElevcHien

G

Fig.4 De+ail cf A

Fig.o De+ail of
S+rap Hinges

Fig.2 Side Eleva+ion

ig.5 De+ail
of B

Each half of the safety gate is bolted by iron straps,
detailed in fig. 3, to the steel siding of the cage. The
bent bars A, of which there are three for each side of
the gate,‘are made of j or 1 in. round stock 4 in. less
in length than the side length of the cage plus one-half
the front width. Each bar is bent at right angles at a
distance from one end equal to 4 in. less than half the
width of the cage, and again at a distance of 2 in. from
the same end, so that the bar has the form shown in
fig. 4. The short right angle bend is threaded to receive
a nut. The other member making up the rest of half
the gate, detailed in fig. 5, is a straight bar of steel B,
f by 2 in., 4 or 44 ft. long, with a handle C riveted or
bolted to it at a convenient height, and with three holes
D for the side bars, which are bolted in as shown in the
illustration. Fig. 1 shows one side of the gate folded
back against the side of the cage, and the other side let
down into position, the lower end of the bar B dropping
into a rectangular slot E in the floor of the cage, a
small steel plate F, suitably slotted, being attached to
the wooden floor of the cage to act as a catch or guide
for the bar B. When folded back the gate is held by
keep G.

* Engineering and Mining Journal.

The Faraday Society.—The Faraday Society, 82, Victoria-
street, Westminster, will hold a general discussion on
“ Refractories " at their first autumn meeting, the date of
which is provisionally fixed for Wednesday, November 8,
1916. The discussion will be presided over by Sir Robert
Hadfield, F.R.S., president of the society, and the opening
paper will be read by Dr. J. W. Mellor, of Stoke-on-Trent.

Coaling in the Panama Canal.—The new coaling station at
Christobal, which has an emergency storage capacity of nearly
500,000 tons, which can be increased indefinitely in connec-
tion with land storage alongside the plant, has been designed
with especial regard to naval uses. Its ability to deliver
2,000 tons of coal an hour to a ship will make it theoretically
possible for a whole fleet to coal there in 24 hours for an
extensive cruise. The plant is of a novel design, made with
a view to just such an emergency.