THE COLLIERY GUARDIAN

AND

JOURNAL OF THE COAL AND IRON TRADES.

Vol. CVIII.

FRIDAY, AUGUST 7, 1914.

No. 2797.

Resins in Palaeozoic Plants and in Coals of High Rank/

By DAVID WHITE.

Introduction.—The theory that coal is but peat,
mainly of swamp types of formation, that has been
transformed by normal geologic processes, seems to have
been completely demonstrated, though it is not fully
accepted by many geologists and chemists. Naturally,
in the process of building up peat those plant parts and
products which were most resistant to the decomposing
agents, principally bacteria and fungi, would survive
longest, and, other things being equal, would be most
easily recognised in the undestroyed debris remaining
in the coal. Among these decay-resisting products are
the resins, waxes, spore covers, cuticles, seed coats, and
bast of the plants of numerous kinds that are contri-
buted to the peat. The fact that the presence both of
the remains of resin-bearing plants and of resin itself in
the high-rank coals of the palaeozoic and mesozoic forma-
tions has not been generally recognised is due to the
nature of the evidence rather than to the lack of it. The
purpose of the present paper is (1) to show that resins
have been contributed to the high-rank coals of the
cretaceous and tertiary periods, as well as to the coals
of low rank which are characteristic of those periods;

(2)	to point out the evidence that the carboniferous
floras were possibly as richly productive of resins or
resinous substances as the floras of later periods; and

(3)	to demonstrate, with illustrations of material both
common and unique, the presence of abundant resinous
material in palaeozoic coals.

Resins in Coals of Low Rank. — The occurrence of
fossil resins in the lignites of the cretaceous period is
known to all who have closely observed these fuels. As
ordinarily observed, without the aid of the microscope,
the resins consist of very irregular lumps ranging from
the smallest particles to fragments over 1 in. in
diameter. The resins are generally yellowish,
brownish, or amber-coloured, translucent, and
vitreously conchoidal in fracture, though some of the
material is pale yellow and apparently granulose in
texture. As is well known, the amber of the arts and
most of the copal of commerce are merely fossil resins,
the greater part of the trade supply of amber having
been produced by several tertiary species of pines now
found fossil in the rocks bordering the Baltic Sea in
Eastern Prussia. Although at some localities and in
certain layers of the lignites and sub-bituminous coals
small lumps of resin may be so numerous as to be con-
spicuous on the bedding planes or cross fractures of the
coal, these are, after all, insignificant in quantity as
compared with the resin in particles of microscopic size
contained in the same layers or even in layers that
reveal no resin at all to the unaided eye. These micro-
scopic fragments are present in varying amounts in
practically all the low-rank coals of cretaceous or tertiary-
age that have been microscopically examined. In some
places they are so abundant as to impart a yellowish or
brownish colour to the layer. The relative amounts of
these resins and resin compounds affect certain impor-
tant qualities of the fuels, as will later be noted.

Concentration of Resins in Coals.—The principle pro-
posed by many of the older palaeobotanists and
emphatically reiterated by Regnault and Bertrand, that
the vestiges or remains of the plant structures contained
in the coals represent, in general, those parts of the
plant or those kinds of tissue which were most resistant
to decay, is exceptionally well illustrated by the resins.
Thus the decay of the less resistant starchy and
cellulosic compounds is followed by that of the more
resistant; the wood succumbs before the corky bark;
the proteids disappear in advance of the waxes, and so
on, until in the most “ mature ” and “ amorphous ”
peats little is left except the most indestructible parts,
such as the resin particles, fragments of cuticles that
are composed of very resistant substances, and the

*From Professional Paper 85 E, United States Geological
Survey.

resinous or waxy coverings of spores and pollen grains.
Of these persistent portions of the plant the resins
generally survive to the last the subaqueous biochemical
or putrefactive processes concerned in the formation of
peats. From the foregoing statements it will be seen
that as the resin is the most resistant to decay, it
obviously will, other things being equal, survive to form
the largest percentages in those peats (coals) in which
the decay of the plant debris has gone farthest. The
successive decay of the less resistant enveloping and
associated tissues gradually frees the resin particles,
which, with the disappearance of the other plant
materials, settle together in an accumulation, really
a natural concentration. Hence a mature or
“ amorphous ” peat formed by the far advanced decay
of plants that have a comparatively low resin content
may actually be much more resinous, as the result of
such concentration, than another peat of the xyloid type,
composed largely of wood which, though relatively rich
in resin, has undergone comparatively slight decay.

c, • ■'

5^.





Fig. 1.—Fragment of Bituminous Coal showing
Carbonised Wood, &c.

Shows bedding-plane surface. The surface is strewn with
small pieces of wood now flattened and converted to mineral
charcoal ("mother of coal”). Most of the pieces are
traversed lengthwise of the grain by needle-like resinous
canal ch sts.

What is said above as to the genesis of peats may be
affirmed also of lignites, sub-bituminous coals, and coals
of higher grades, all of which are but lithified and altered
peats.

Effects of Resin Concentration.—It has often hap-
pened during the formation of thick deposits of peat
in a swamp that the water has in places been for a time
too deep to be occupied by vascular plants growing
in place. In these pools, sometimes small and irregular
in form, where the water was temporarily open and the
supply of oxygen was greater, the decomposition of the
vegetal debris falling into the water could, if the water
was not too stagnant, go so far as to leave only great
quantities of resinous matter mingled with spore and
pollen exines, wax residues, and cuticles. The same
condition could exist also beneath the ordinary shallow
water cover in portions of the swamp if the oxygen
supply was sufficient and the rate of accession of fresh
plant debris was not too great. Layers of such matter
may be recognised in many coals, though usually they
are thin and obscured by underlying or superimposed,
more or less coarse vestigial matter. They form the
“ fatty ” parts of the bed. When the deeper water body
was restricted, steady, and sufficiently stagnant to pre-

clude the inwash of considerable mineral sediments and
the complete destruction of the organic vestiges, and
the spore, pollen, wax, and resin concentrate was there-
fore low in ash and comparatively unstratified, the
resultant “ sapropelic ” deposit is canneloid—that is,
it forms canneloid layers or lenses—in the lignites, and
these layers or beds, when the lignites were changed to
coals of sub-bituminous and higher ranks, became cannel
coals and oil rocks, though the latter, being generally
formed in water bodies of greater extent and supposedly
carrying innumerable algee of low orders, and containing
more mineral matter, are usually high in ash. The
origin of the cannel type of coal is, in its essential
features, the same without regard to the geologic age of
its formation or the rank of the fuel, though the mutual
proportions of the characteristic components, exines and
resins*, may vary from place to place and from epoch
to epoch. The concentrated resins and the resinous and
waxy exines of. the pollen and spores, variously mingled
with microplankton vegetal elements, impart to the
coals of the cannel and oil rock group their high volatile,
high heating, and high illuminating qualities and their
tendency to fuse, even if they are of low rank, the
resins and waxes being characteristically rich in
hydrogen, the element of greatest calorific value, and
relatively low in oxygen, the great heat nutraliserf in
coals. The canneloid coal is high in volatile matter
merely because its component plant remains or products
are not only high in volatile, but resistantly so. It
will readily be seen that the presence of resins and spore
and pollen exines must have its effect on all coals, the
result being more conspicuous when the proportion of
cannel forming elements is greater. A high hydrogen-
oxygen ratio (“ pure coal ” basis) in a coal below the
semi-anthracite rank is to be regarded as indicating a
more distinctly “ bituminous ” type of coal, for the
bitumens are especially characterised by their very h.gh
hydrogen and their correspondingly low oxygen content.

The Obliteration of the Resins.—It is important when
discussing the origin of coal to recognise the operation
of two great and fundamentally distinct processes or
stages. The first process is the biochemical, which
accomplishes the transformation of miscellaneous
vegetal debris into peat. The second process, which
follows or perhaps slightly overlaps the first, antedating
the complete cessation of anaerobic bacterial action, is
dynamo-chemical. Through the action of the dynamo-
chemical agencies, apparently initiated and dominated
in general by pressure, but sometimes immediately con-
trolled by contact-metamorphic heat, the peats have
been transformed to lignites and coals of all higher
ranks. In this progressive transformation, what
becomes of the resins and waxes? The answer to this
question depends largely on optical evidence. Lump
resins in widely varying amounts were found in all the
lignites and sub-bituminous coals examined, though
in many coals the pieces were very small. It is not
probable, however, that the resins of these coals have
remained wholly without chemical change from their
original composition, notwithstanding their typically
resinous appearance. In the higher-rank coals—that is,
in those grading through the lower bituminous ranks—
the resins are found to have changed very greatly, having
evidently undergone both physical and chemical altera-
tion. This is shown in general, first, by the darkening
of the colour to a smoky brown; later, by the further
blackening, crackling, and shrinkage of the lumps,
which at a still later stage appear to be reduced to dark
brownish-black spongy or granular residues, and still
later, if the observations are correct, to a thin, fine,
powdery black scale. The last state is difficult of
recognition, and its correlation with the resin lumps is
not without question. This change of the resins, which
constitutes in effect a reduction (carbonisation) of the

* The term "resins” is here under in the broad sense,
though in the later descriptions of fossil specimens
it signifies the characteristic “ rosin ’’-like and amber-like
resins.

t See White, David, “ The Effect of Oxygen in Coal ” :
U.S. Geol. Survey Bull. 382, 1909; Bureau of Mines Bull.
29, 1911.