John Pinkerton.

Petralogy. A treatise on rocks (Volume 1) online

. (page 34 of 35)
Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 34 of 35)
Font size
QR-code for this ebook

like many other useful improvements, derived
from our commerce with the Flemings *.

Even in the same bed the coal is seldom of the
same quality, or homogenous ; so that many of
the German subdivisions would, in the case of
any other substance, be regarded as mere varie-
ties. Such is the fibrous coal of Estner, which
was brought from Newcastle ; the ribbon coal
of Irvin on the western coast of Scotland ; the
parrot coal, said by some to be so called from its
iridescence, while others suppose that it received
its name from the crackling noise it makes when
first kindled. It is surprising that Werner has
not arranged the earthy coal, called smut or
culm, as a distinct subspecies. It has been ob-

* According to Buffon, Min. i. 478, 4to. the deepest coal mines
are those of Namur, 2,400 feet.

2 P 2


served, that where the coal approaches the slip,
it has lost its bitumen, whence it is argued, that
the slip rose heated from beneath ; while others
only infer, that the bitumen has been absorbed
by the humid rock. In confirmation of the for-
mer opinion, it is added, that in the north of
Ireland the layers of flint become red and light
when they approach the whindyke ; and speci-
mens which I have seen, certainly bore every
mark of having been affected by great heat,
iridescent. The iridescence of coal often penetrates a large
mass, and appears in almost every direction. In
the peacock coal of Wales or Somersetshire, this
iridescence often assumes a strong resemblance
of what are called the eyes in a peacock's tail *.
In that of the valley of Llangolen,the iridescence
consists of steel-purple, crimson, green, yellow,
and blue, disposed in zones. But by far the
most beautiful of this kind, is a coal found in
small portions, near Valenciennes, in which
crimson, green, blue, and yellow, perfectly opa-
lise or interchange; so that the substance has
more splendour than even the noble opal. The
exquisite vivacity of the tints can only be equal-
led by some of the celebrated iron ores of Elba;

* Mr. Parkinson, Org. Rem. vol. L, informs us that peacock
coal is found in Somersetshire at a considerable depth, the surface
being mingled with fossil shells, and vestiges of fern.


and probably, on a chemical analysis, these
kinds of coal would be found to yield a small
portion of iron and sulphur.

The structure of coal, as already mentioned,
may be regarded as universally schistose: and it
is believed that even the columnar may be con-
sidered on a large scale, in the same point of
view, that is, the columns are horizontal, and
piled like billets of wood on each other. The
small columnar kind found in Scotland, consists
of little columns, about half an inch in diame-
ter, and a few inches in length, united in a com-
mon base *. Its form seems to arise from the
ferruginous gangart, which envelopes, as in a
sheath, the little columns of coal; and it is like-
wise said to occur in a form merely schistose.
It is in fact so minute as rather to belong to li-
thology. The chief variations of coal can there-
fore only be classed as aspects.

Aspect 1. Common coal This substance is
only observable when it presents some remarkable
diversities, is accompanied with singular accidents,
or is brought from new regions.

* Mr. Jameson, Dumf. 160, says it is found about four miles
from New Cumnock, Ayrshire, along with graphite, which is also
sometimes columnar.


Coal from Australasia.
The same from China.
The same from Cape Breton.
Ribbon coal, from Irvine, Scotland.
Peacock coal, from Wales, or Somersetshire.
Opaline coal, from Valenciennes.
Coal with calcareous spar, from Derbyshire.
With lead, from Buckinghamshire.
With foliated pyrites, and white veins of calca-
reous spar, from Derbyshire, Sec.
With antimony, from North America.
With cinnabar, from Idria.
With copper ore, from Saxony.
With native silver, from Hessia.
With gold, from Silesia.

Aspect 2. Laminar or Foliated.
From Saxony and Silesia.
From the mines of Wodensbury, or Winsbury,
in Staffordshire. It is commonly of inferior quality.

Aspect 3. Cannel coal. This occurs in more
thick and compact layers, and the fracture is some-
times even, sometimes large and flat conchoidal.

Cannel coal, from Lancashire and Shropshire.

The same, from Gilrnerton and Muirkirk ; in


Aspect 4. Columnar'coaL

As the German kind belongs to anthracite, so
it is probable that the Scotish is of the same de-
scription ; the latter, however, presents the velvety
appearance of the charcoal plates in common coal ;
but is so deeply impregnated with oxyd of iron,
that it is partly of a brown, partly of a metallic
lustre ; which may not only be the cause that it
does not flame, but is probably the original source
of its columnar form, which iron often affects ; and
as the power and predominance of that metal are
very great, it often manifests its presence, by in-
ducing almost any other substance to assume its


This name has been assigned, with great pro- Name,
priety, by Brongniart to the substance which
Werner has called brown coal, with his usual at-
tachment to colours, which of all denominations
are the most vague and illusory. Some who
prefer Greek etymons might call it xylite, de-
rived, in like manner, from wood; but the Latin
language is equally classical with the Greek, and


is of general use in the definitions of natural his-
tory ; so that there seems no reason for its ex-
clusion, while on the contrary its admission af-
fords a pleasing variety.

The account of lignite, given by Brongniart,
is so complete, clear, and satisfactory, that it
shall be translated with a few subjoined observa-
tions ; after premising that one of his varieties,
namely jet, rather belongs to lithology in every
sense, as it is found in small pieces, and only ap-
plied to minute purposes of use or decoration.

The others are found in large beds or masses,
by the Germans called bergarts ; and though
many rocks are composed of shells, corals, ma-
drepores, and other animal remains, the reader
might be startled at the idea of a rock composed
of wood. Yet rock-salt, which will be treated
among the Anomalous, perhaps affords an idea
little less incongruous ; and too great precision
would lead to neology, which ought always to
be avoided, except in cases of indispensable ne-
cessity. Rocks of pumice or of obsidian, or even
of topaz, are ideas equally new to the generality
of readers, yet they exist in nature, which must
be followed, and not controlled.
Brongniart's cc The combustible minerals which belong to


this species, are characterised by the odour, and
the products of their combustion. The odour


they spread in burning, is pungent, often fetid,
and has no analogy with that of coal or bitu-
mens. They burn with a clear flame, without
bubbling or caking like coal, or running like so-
lid bitumens. They leave powdery ashes like
those of wood, but often in greater quantity,
more ferruginous, and more earthy : they seem
to contain a little potash *. These combusti-
bles give an acid by distillation, which coat does

<c Lignites vary in colour from deep and
shining black, to an earthy brown : the texture
of the greater part of the varieties indicates their
origin, and gives rise to their name. The woody
tissue is often observed, though sometimes it has
wholly disappeared. The fracture of lignite is
compact, often resiniform and conchoidal, or
shining and straight.

" The external characters of the varieties of
the species differ too much among themselves,
to allow them to be farther generalised.

" 1. Lignite jet f. It is hard, solid, compact,
and capable of receiving a very bright polish ;
it is opake and of a pure black ; its fracture is
undulated, and sometimes shining like that of

" * M. Mojon found about 3 in 100 in the ashes of the bitu-
iminous wood of Castelnuovo.

" f Jet, Haiiy Pechkohle, piciform coal. Broch"


pitch. Its specific gravity is 1,259. It is said
to be sometimes lighter than water *.

" This variety is found in layers of little thick-
ness, in marly, schistose, calcareous, or sandy
beds. The organic tissue of wood is sometimes
observed in it.

" This lignite is found in France ; in Pro-
vence ; at Belestat, in the Pyrenees ; in the de-
partment of the Audef , near the village of Bains,
six leagues to the south of Carcassone ; this
sometimes contains amber ; and near duilian,
in the same department, in the communes of
Ste. Colombe, Peyrat and Bastide ; it is at the
depth of 10 or 12 yards, in oblique layers, be-
tween beds of sandstone; but these layers are
neither pure nor continuous. Jet, proper to be
worked, is found in masses, the weight of which
seldom exceeds 50 pounds. These mines have
been wrought for a long time, and have pro-
duced a considerable quantity of jet, which is
cut and polished in the same country.

" In Germany, near Wittemberg in Saxony;
it is also there wrought and polished. Very
fine jet has been found in Spain, in Galicia, and

" * I doubt if real jet be ever lighter than water. This property
seems rather to belong to the next variety."

f An account of the manufacture of jet, in the department of the
Aude, may be found in the Jour, des Mines, No. 4, p. 35. P.


in the Asturias. In short, it is mentioned as oc-
curring in Iceland, in the western part of that

cc Of this combustible, ornaments are made,
particularly mourning trinkets. Jet is polished
with water, on a wheel of sandstone, worked ho-
rizontally. Jet, mingled with pyrites, is generally

" 2. Friable lignite *. This variety is found
in extensive and thick beds ; it is of a bright
black, but less bright than the preceding kind;
what above all distinguishes it, is its great fria-
bility ; its surface is always cracked, and its mass-
es are divided, with the greatest facility, into a
number of cubic pieces, a character which lig-
nite jet does not present. In some instances,
the tissue of vegetables, which have formed it,
is observable.

" Friable lignite is more abundant, and con-
sequently more useful than the two first varieties.
It is found in horizontal beds, often thick and
extensive, but is never found in such large mass-
es as coal, with which it .has very improperly
been confounded. It not only differs by its pro-
perties, but it also differs in its locality. It is
found in masses of sand, which often fill calca-

" * Moorkohle, mud coal Brock:'



. reous valleys, or which lean against the hills
which skirt them. It is also found, but more
rarely, in argillaceous marl.

" This combustible is common enough in the
south of France, particularly in the department
of Vaucluse. I have found it under the circum-
stances I have just mentioned, at Piolin, near

" It is found in very large mass, at Ruette,
department of the Forests.

" It easily burns, but emits a very disagree-
able odour. It can only be used in manufac-
tures, and to burn lime. Smiths cannot use it
in their forges.

" 3. Fibrous lignite *. Its colour varies from
a clear blackish brown to a clove brown. It
has a perfect woody form and texture, conse-
quently its longitudinal fracture is fibrous, and
in its transverse fracture are perceived the annual
circles of the wood.

" It is easier to break than wood ; under the
knife it assumes a kind of lustre.

" This lignite is sometimes found in consider-
able masses.

" It is found in France, in the neighbourhood
of Paris, near St. Germain, in the isle of Chatou,

t( * Gememer~lituminoses-holz, common bituminous wood.


which seems to be entirely formed of it; and
near Vitry, on the banks of the Seine, there is
a thick bed of trunks of trees well preserved
(Gillet Laumont). In the department of Arriege,
the clefts of this lignite are penetrated with
sparry carbonate of lime. In Liguria, near Cas-
tel-Nuovo, at the mouth of the Magra, it is in
thick and very extensive beds. In Hessia, near
the mountain of Ahlberg, the layer is two yards
thick. In Steinberg, near Munden in Hanover,
it forms two layers, one 10 yards, and the other
six, which are separated by a bed of rock from
12 to 14 inches thick. In England, at Bovey
near Exeter, there are 17 thick beds, which are
at a depth of about 66 feet, under sand, and in
potters clay. In Iceland it is very abundant,
and is called surturbrand ; the trunks which
form these heaps are very distinct, and seem
merely to have been compressed.

" But this lignite is still more common in little
detached masses ; sometimes it accompanies the
preceding varieties ; sometimes it is found alone,
in small layers, in the midst of beds of argil or
of sand. It is met with almost every where, and
is used as fuel in those places where it is abun-

" This vegetable, rather than mineral com-
bustible, being scarcely decomposed, would not


deserve to form a variety in the systems of mine-
rals, if it did not pass by imperceptible degrees
to the varieties which precede it, and to that
which follows. Its history, in strict language,
more properly belonging to geology, than to

" " Earthy lignite*. This substance is black,
or of a blackish brown, mingled with a reddish
cast. Its fracture and aspect earthy, fine grain-
ed, rather soft, even friable, smooth to the feel,
and becomes bright by scraping. It is nearly
as light as water. It burns, emitting a disa-
greeable smell.

cc It not only often contains remains of vege-
tables, but sometimes itself presents the texture
of wood, without ever possessing either the co-
lour or brightness, or the hardness of the pre-
ceding varieties.

" Earthy lignite, burns sufficiently free to be
used as fuel ; it gives a gentle and equal heat,
but exhales an odour generally unpleasant, but
sometimes rather agreeable.

" It is found sometimes in the midst of secon-

" * Biiuminose hoherde, earthy bituminous wood. *Broch.
Vulgarly earth of Cologne, and sometimes, but improperly Umler.
Umber, properly so called, which comes from Italy, or the East,
containing nothing thai is combustible, cannot belong to this spe-


dary earths in the neighbourhood of coal mines;
sometimes, and even most often, in alluvial land.
4C We shall mention, as an authentic example
of this variety, the earthy lignite of the environs
of Cologne, known in trade by the name of earth
of Cologne, as it is wrought at a little distance
from that city, near the villages of Bruhl and
Liblar. This lignite forms very extensive beds
of eight or ten yards in thickness, which are si-
tuated under considerable elevations. It is im-
mediately covered with a bed, more or less thick,
of rolled pebbles of quartz and jasper, as large
as eggs, and reposes on a bed of white argil, of
an unknown thickness. The bed of lignite is
homogenous ; but fossil vegetables are found in
it, very well preserved. They are, 1. Trunks
of trees, lying one on the other, without any
order, the wood being black or reddish, generally
compressed : they easily exfoliate, by drying in
the open air. Some belong to trees of the dico-
tyledon kind, others are fragments of palm-trees.
Among these, M. Coquebert-Montbret has found
some which are full of small round pyritic bodies,
resembling grains of small shot *. This wood

" * M. Heimhas remarked in the lignite of Kalten-nordheim, in
Thuringia, small elongated spherical substances, resembling a pod
of two partitions. M. Blumenbach supposes them to be unilocular
bivalve capsules. (Journal des Mines, No. 105.)"


burns very well, and even with a kind of flame.
2. Woody fruits, the size of a nut, and which
have been known to be those of a species of the
palmtree (areca). The lignite of Cologne con-
tains about 0,20 of ashes, rather alcaline and
ferruginous (Ant. L. Brongniart.) Its uses are
various; it is worked in open air with a simple
spade ; but the more easily to transport it, it is
wetted, and moulded in vases, which give it the
form of a truncated cone.

" It is used as fuel in the environs of Cologne.
It burns slowly but easily, and without flame,
like tinder, giving a lively heat, and leaving very
fine ashes. These ashes being considered as a
very good manure, to obtain them a part of
this lignite is burnt on the spot where it is
wrought. .

" Earth of Cologne is more especially used
for painting in distemper, and even in oil co-
lours. The Dutch use it to adulterate their
snuff; when it is not mixed in too great a quan-
tity it gives the snuff a fineness and softness,
which is much esteemed, and cannot be in the
least injurious. (Faujas.)

" This lignite is also said to be found in Hessia,
Bohemia, Saxony, Iceland, &c. (Brochant); but
as there has been a confusion between this com-
bustible and the variety of ochre, called umber.


we cannot be positive that these local indica-
tions have really any relation to earthy lignite.

" It may have been observed, from what has
been just said on the situations peculiar to some
varieties of lignites, that this fossil combustible
belongs to soils of the most recent formation,
since it is only found in accretions of sand or
argil. It is almost never met with under rocky
beds, except in coarse carbonated lime, and un-
der basalt. In the mountain of Ringe Kuhle in
Hessia, several thick layers of lignite are ob-
served, lying on a sandstone, and separated by
layers of potter's clay and sand (Mohs). Oa
the sea shore, near Calais, fragments of lignite
have been picked up, which were penetrated
with crystals of quartz, very limpid, and disposed
in spheres.

" Lignite then is of a very different formation
from that of coal ; and M. Voigt thinks that
there is no transition between those two com-

<c The air which circulates where lignite is
wrought is generally bad*."

In his Essay on Geology, Faujas has given an of Cologne.
accurate and ingenious account of the prodi-
gious mass of lignite near Cologne,which extends

* Bronga. u< 30.

VOL. r. 2 Q


for many leagues, and is covered with a bed of
pebbles from 12 to 20 feet in thickness, while the
lignite itself exceeds 50 feet*. Our ingenious
observer says that the trunks of trees, which
are often found, are always deprived of their
branches; whence he argues, that they have
been conveyed by the ocean. Besides the nuts,
which now belong to Hindostan, the Moluccas,
and China, masses of a kind of gum or frankin-
cense are found, which when burnt perfume the
huts of the peasants f.

Masses of a similar kind have been found in
many quarters of the department of the Aisne;
one of the most remarkable being that near
Beaurieux, where a pit sunk to the depth of 65
feet, ended in a subterranean marsh, full of sand
and water, which soon filled the pit J. In that
of Villers- en-Prayer, at the depth of 17 or 18

* i. 410.

f There is in Prussia a mine of amber, 98 feet deep, and the am-
ber is found between two salbands of lignite, and sometimes adhe-
rent. Jour, de Phys. tome xxxix, p. 365. At Vorospatac, in
Transylvania, a lignite is found with leaves of gold. Journ. de$
Mines, No. 23, p. 83.

I In Mount Meisner, Hessia, there is a very thick bed of fossil
turf, with trunks, branches, and roots of trees, reposing on lime-
stone, and covered with basalt. De Luc, Geol. 339, thinks that
such hills had sunk under water, and were again elevated. At
Schemnitz there is a vein of lignite at the depth of 360 yards. Journ.
des Mines, iv, 807.


feet, a lignite was found much impregnated with
pyrites, as are most others of the Aisne. In this
bed of decomposed wood, which is about three
feet six inches in thickness, are found pieces of
fossile wood, partly carbonised ; some bones of-
animals, seemingly of wild kine; amber in round
or angular fragments, some quite transparent
and sometimes imbedded in pyrites. Such vene-
rable relics must not be confounded with peat,
which commonly proceeds from the decompo-
sition of graminous and other small vegetables,
though trunks, hazel nuts, &c. be occasionally
found. Faujas supposes with Patrin, that coal
itself may often consist of wood brought by the
sea, and deposited in recesses at considerable
elevations, when the globe was studded with pri-
meval islands. The numerous sea plants, mo-
lusks, and oily carcases of so many fish that
daily perish, also contribute, in his opinion, to
this product; but this theory has many diffi-

Professor H oilman of Gottingen, published in
1784 an account, which had before appeared in
the Philosophical Transactions, vol. 51, of some
hills or mountains, as he calls them, near the
city of Munden, and in that point of land which
is washed at their junction by the rivers Werra
and Fuldaj one is about 1150 feet in height,


and they may be said almost to consist of fos-
sile wood. Another near Altendorf, on the bor-
ders of Hessia, about 1800 feet in height, pre-
sents vast quantities of fossile wood, under a stra-
tum of stone, not less than from 80 to 140 yards
in thickness *.

Bovey coal. One of the most remarkable lignites is the Bo-
vey coal of England, already mentioned. Dr.
Kidd observes, that it is attended with a kind of
porcelain clay, derived from the waste of the
adjoining granite hills, subsiding into this heath,
which is a natural basin f. The sandy quartz,
and fragments of felspar, correspond with those
of the adjacent granite. This lignite often rises
in the form of trees, but is often compressed in
straight flat pieces, three or four feet in length,
which are called board-coal, from a natural re-
semblance 5 an observation which may also be

* Parkinson, Org. Rem. vol. i. He supposes that petrified wood
passes through a bituminous fermentation, after which it is saturated
with water full of siliceous particles. See also ii. 285, where he
adds, that animal matter, by long residence in water, was first con-
verted into the adipocere of Fourcroy, resembling spermaceti. This
ingenious writer has also observed, i. 364, the presence and in-
fluence of bituminous matter in the semi-opal, and other stones of a
ivaxy lustre ; so it may enter into the opal. But as Klaproth only
found inflammable matter, may not the carbon, which forms a large
proportion of bitumen, here exert its power?

* Outlines, i. 166.


extended to the surturbrand of Iceland. Mr.
Hatchet has, with his usual acuteness and ability,
examined many similar substances, as the wood
of the submarine forest, off Sutton, on the coast
of Lincolnshire, which he found yielded kali, and
had no character of coal. An analysis of 200
grains of Bovey coal yielded water 60, thick
brown oily bitumen 21, charcoal 90, * mixed
gaz 29.

The presence of the substances, called by the Origin,
chemists extract, resin, and fibre, are esteemed
to evince the original vegetable character, how-
ever it may be transmuted or disguised. The ex-
cellent experiments of Mr. Hatchet, demonstrate
that the extract is the first principle that disap-
pears, next the resin, and lastly ihefflre. When
every mark of organisation has thus disappeared,
the substance becomes compact, and the con-
choidal fragments resemble pitch*. In this
new condition it is called coal, to which the lig-
nite of Bovey nearly approximates. In the
strata of this substance, Mr. Hatchet also ob-
served small masses approaching to the nature of
the lignite of Cologne, and which he called re-
sinasphaltum, or resinasphalt, as it contains about
55 of resin, and 41 of asphalt.

* Ib. ii. 42.



Aspect 1. Entire. Bovey coal.

Surturbrand, from Iceland.

Fibrous lignite, from France, Liguria, &c.

Aspect 2. Mingled. Bovey coal, with resinas-

Lignite, with amber, from Prussia.


From the south of France.


Aspect 1. Entire. Umber or earth of Co-

Aspect 2. Mingled. The same, with nuts re-
sembling the areca.

With a gum which burns like frankincense.

Having thus described the ESSENTIAL ROCKS,
or those which receive their divisions and deno-
minations from preponderant or from predomi-

Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 34 of 35)