76

THE COLLIERY GUARDIAN

January 8, 1915.

The Formation of Coal Seams.

Micrographical Researches,

At the last meeting of the South Staffordshire and
Warwickshire Institute of Mining Engineers, a lecture,
copiously illustrated by micro-section lantern slides, was
delivered by Mr. Jambs Lomax, of Great Lever, Bolton,
on “ The Formation of Coal Seams in the Light of
Recent Microscopic Investigations, and its Influence
on Modern Mining Problems.” The lecture had
reference largely to the local measures of Staffordshire.

In the course of his lecture, Mr. Lomax referred to
his work on the subject which has already been
published, and observed that every coal seam that he
had examined so far showed that it had been laid down
in laminae, or layers, which had a natural and orderly
sequence, and from these layers or lamin® one could
tell practically the character of the plants from which

Fig 1.

tion, and becoming the predominant plants of their time.
That went on for a length of time, but just as had been
seen in various geological horizons in animal life, so
plant life, when it had made a certain amount of
progress in one direction, began to deteriorate, with the
result that the aspect of life became changed altogether.
So it was in a coal seam. The various changes,
progress and deterioration, could be traced, until
ultimately the plant life represented in the top of the
seam was found to be practically like that at the bottom.

The Shallow Seam.

Dealing with the slides he put on the screen, the
lecturer pointed out that in the Shallow seam it could
easily be seen, by the series of vertical sections, that

Fig. 3.	Fig. 5.

shown in figs. 3 and 4), there being also a fair amount
of leaf tissue, etc. One thing which he wanted to
point out was that very often a part of a seam was
prone to spontaneous combustion. They would notice
that in some parts, especially on some of the last slides,
the coal was more or less cracked. He had experi-
mented with pieces of coal which had been sent to him
direct from the pit in boxes packed so that no air could
get to them, and that they could not by any chance be
knocked about. As already mentioned, there occurs
bands of a dull bony-looking appearance, alternation
with bands of a variable thickness being bright and
jet-like. Many of the latter are composed of com-
pressed portions of stems of various species. Above
and below one of the bright bands may occur the dull
bands, as will be noticed in photo-micrograph shown
in fig. 5.

Resinous Bodies.

It will be noticed that the bottom band, which is the
bright, is full of irregular cracks, whilst the band above

Fig. 7.

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Fig. 6.



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(Sterng.) with Fructiferous Branches and
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the debris had been derived. The investigation com-
menced at the bottom of a seam, and it was found in
all cases so far, that this part of a seam was more or
less homogeneous, having little difference between one
part and another. Usually, the lower part of a seam
consisted of a bed of very fine humus, or mixture of
leaf-like matter, with here and there portions of stems,
fructiferous organs, etc., probably derived from the
remains of small plants, this forming a soft, bright
looking bed of coal. Ascending higher up the seam,
remains are found of “ cordaites,” a type of plant
belonging to the gymnosperms, a genus embracing firs,
eycads, and other allies of recent times. Then there
came in another race of plants, the lycopods, which as
time went on increased both in size and vigour, ulti-
mately crowding out almost every other kind of vegeta

Fig. 9.



this seam commenced and ended in the same manner,
with the remains of cordaites, and it must have taken
a great length of time for the intermediate changes in
the character of the vegetable growth to have developed.
In the Cockshead seam, in North Staffordshire, one
found a material difference altogether from that in the
Shallow seam. The thickness of the Shallow seam was
7ft. 6in., and he had only examined about 5ft. of it.
A pillar of coal he had taken from the colliery again
illustrated what he had tried to explain by the photo-
micrographs he had brought with him. The pillar was
taken from the well-known Hard Mine seam at Longton.
They would see at the bottom of the seam there was
practically no lamination, but the coal at the bottom
w<as more or less composed of fine humus, bright
looking, and the laminations began to appear with the
very bright bands in between. This went on until a
little higher nothing remained but the fructiferous
organs of the lycopods or club mosses, namely, the
megaspores and mierospores. In portions above were
to be seen the remains of cordaites and some other
higher plants, which were allied to plants now living.
As one went further up the seam, they found these
gradually squeezed out by the return of the smaller
plants and lycopods, until ultimately at the top of the
seam one got nothing but the minute remains of a
similar character to those found at the bottom.

In the micrograph showing the bottom portion of
the Shallow seam would be noticed here and there long
ribbon-like bodies, and also a little higher up some
bright bands. This bottom portion was composed of
the remains of equisetin®, ferns, and plants of a similar
character. As one got higher these bands became
thicker, some being the flattened stems of calamites.
In fig. 1 they would see that these had been
flattened out, or, as he called it, “ jetonised ”—made
almost like jet. Surrounding these spots were to be
seen little mierospores, which became larger and larger
as time went on, and then began to grow smaller and
smaller, and finally died out. In the portion of the
seam about 10 in. from the floor would be seen leaves
lying one on the top of another, these being the leaves
of cordaites. Many of these leaves, both in vertical
and horizontal sections, show the vascular tissue of the
leaves almost perfect, also alternating bands and
lamin® of microspores, megaspores, and other vegetable
debris lying layer on layer in perfect order. A hori-
zontal section from this region shows both leaf tissue
and megaspores together (see fig. 2) (Mag. x 6). In
the portion of the seam a little higher up can be seen a
great increase in the remains of the fructiferous organs
of the lycopods. In this region both the megaspores
and microspores are exceedingly well preserved (as

is free from cracks. It will be readily seen the reason
for this. On taking a piece of coal similar to the
above, cutting from it a slice, or making on the sample
a flat surface at right angles to the bedding planes, it
will be found that in a very short time the bright
looking portions are full of cracks, whilst the dull
portions are intact. In the dull looking portion there
has, however, been some alteration. There has been
an expansion of these parts, causing a series of ridges
or unequal swelling. This can easily be proved by
getting a perfectly flat surface of a piece of coal, and
allowing the piece to stand for some time, and then
putting a straight edge on the flattened surface. The
above action occurs at the ordinary temperature, but if
the sample is heated artificially, the action is more
pronounced, according to the heat used, till ultimately
the bright bands are completely broken up. The
explanation is that the dull bands are composed of
substances of a more highly resinous nature than the
bright bands. The dull bands can either be composed
of microspores or megaspores, or resinous bodies such
as are seen in fig. 6. The coal, which on being freed
from the normal pressure in a seam, allows the more
resinous bands to expand, whilst the less resinous
bands are cracked and pulled asunder through the
unequal expansion, this varying according to the
temperature at which it happens to be. The above process
he believed to be one of the chief causes of coal falling
into slack and dust. The two photo-micrographs
given in figs. 7 and 8 show how the coal becomes
broken up, and the more or less basaltic form the
fragments assume.

In the Shallow seam, as well as in the others that
have been examined, there occurs in various horizons
generally in the soft or fuzzy bands, especially in the
upper part, large numbers of shot-like bodies invisible
to the naked eye. These bodies are not unlike the
“ globulites ” in shape and form which were described
in the Transactions some time ago. They are black,
and often associated with thin veins and strings of
pyrites; there may be thousands of these bodies
disseminated in a cubic inch. Photo-micrograph fig. 9
shows a cluster of these bodies from the Shallow seam.
Bodies of this kind may be a contributing force, if not
a cause of heating under suitable conditions in a seam
of coal.

The Influence of Colour.

The lecturer then exhibited a series of slides illus-
trating the various plant structures and other features
of successive portions of the seam from the bottom
upwards, including some interesting examples of tree
stems, and said that it. was evident that droppings from
plants of various kinds must have helped very greatly,