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tra P* ^^ e va ute f tne Drac, a torrent which
throws itself into the Isere beneath Grenoble, also
belongs to this division. The base, according to
Patrin, is of trap, mingled with clay, or what the
German mineralogists would call a wacken, being
of a grey or violet colour, with spangles of felspar
and globules of calcareous spar; sometimes also
with globules of green steatite* In like manner the
toad-stone of Derbyshire is occasionally, though
rarely, of a light brown colour, with green spots.
Saussure regards the variolites as primitive rocks;
but Werner only classes them as either transitive
or stratiform.

Black amygdalite, or toad-stone, from Derby-
shire.

The same, with veins or nodules of red jasper.

Dark brown toad-stone, from the same.

Light brown, or fawn-coloured toad-stone, with
green globules, from the same.

Variolite of the Drac, the Hartz, &c.

The calcareous spar sometimes decomposes,
and leaves a false appearance of lava.



MODE X. IRON-STONE.



STRUCTURE III. AMYGDALITE WITH OPEN PORES.

This substance abounds in the high upland of
Mexico, where it is of a reddish colour, and is the
tetzontli used in building. As that region abounds
with volcanoes, it is probably a lava.



MODE X. IRON-STONE.

Texture, compact, granular or earthy, some- characters
times undulated. On the surface of English
hills composed of this substance, it often pre-
sents a singular ornamented appearance, as if
derived from pinnae, or some other long py-
ramidal shell, with transverse bars ; and is some-
times covered with yellow rust from the decom-
position of the iron.

Hardness, basaltic. Fragments, amorphous,
rather sharp.

Weight, siderose.

Lustre, dull, opake.

This substance forms many small chains of Sites
hills in England, as in Surry, &a and in other
countries, yet has scarcely been identified in
books of mineralogy. Ferber, in his orycto-
graphy of Derbyshire, mentions iron-stone as



DOMAIN 1. SIDESOUS.

composed of a bluish heavy clay, with an ap-
pearance of containing much iron; he also men-
tions a brown kind, found in the coal-mines of
Stansby. This rock contains from 20 to 40 of
iron, and when rich in that metal is worked as
an ore ; being a Gmieiner Thondscustdn of Wer-
ner, which contains about 40 parts of iron in the
100. But none are here intended to be included
which exceed 20 or 25. It is supposed gene-
rally to indicate coal ; and if so, that mineral
may be expected in Surry. The clay-stone, or
argillaceous iron-ore, has commonly a brown or
red appearance; while this is grey or black,
and probably contains no more iron than basalt.
The name iron-stone is commonly used in Surry
and other counties ; but it probably is one of
the vague whins of the North. It is o i I!K;
gangart of prehnite*.

STRUCTURE I. OMPACT.

Iron-stone, from Surry, Shropshire, &c.

The same, with prehnite, from Dunbarton, &c.

* Mountains of iron-stone exist in the East, if we credit A rub,
Nights, vi. 239, of Dr. Scott's edit. 1811.






MODE X. IRON-STONE. Q7



STRUCTURE II. COLUMNAR.

Mr. Sowerby possesses in his valuable museum
a curious example of this kind, being quadrangular
columns of iron-stone passing through slate.

STRUCTURE III. VARIEGATED.

This kind, with an appearance of shells, &c.
has been already mentioned.

The rock upon which the Capitol of Rome was R k of the
founded, is thus described by Breislak. 1. The
colour is brick red, but with spots of a deeper
tinge, and which are also of a larger grain. 2. Its ,

hardness surpasses that of tufa, but is inferior to
that of lava, being comparable with that of the
freestone used at Paris. 3. If large pieces be
broken off with the hammer, the fracture is even
conchoidal ; in small the fracture is unequal, small
grained, but never rough. 4. It acts on the mag-
netic needle at the distance of two or three lines.
5. It contains scales of mica, fragments of felspar,
and white globules of calcareous spar, with some
fragments of melanite. 6. Observed in the sun
with a good lens, the whole mass is found to be
crystallised.

If this rock be not a red basalt, it may pass

VOL. i. H



98 DOMAIN I. SIDEROUS.

into the Mode of Iron-stone, as appears from its
action on the magnet.

The stone which serves as a gangart to the
quartz crystals called Bristol diamond, may also
be ranked in this division ; but it seems to be only
a vein-stone passing through limestone. Various
kinds of iron-stone, siliceous and argillaceous,
often occur in mines, but have not been found to
constitute rocks.

The following substance may also be added to
this division.

Ironclayof tt j rr . n ~| Q , r
Werner. lron cla Y*

" Eisenthorn. Werner.

" External Characters.

" Its colour is commonly brownish red, which
seldom approaches to blood red, but more often
to reddish brown.

" Occurs almost always vesicular, sometimes
with empty, sometimes with filled vesicles.

" Internally it is dull.

" Fracture fine, earthy, sometimes inclining to
conchoidal.

" Fragments indeterminately angular.

"Is soft, but sometimes passes into semi-hard.

" Is not particularly difficultly frangible.

" Not particularly heavy, in a middling degree.



MODE XI. JASPER.



" Geognostic Situation.

11 It belongs to the floetz-trap rocks, and con-
stitutes, like wacken, the basis of amygdaloid.

" Observations.

" It is distinguished from wacken by its colour,
and the greater proportion of iron which enters
into its composition.

" 2. The iron which it contains is very much
oxydised, whereas that in basalt is slightly oxyd-
ised>*



MODE XI. JASPER.

Texture, very fine grained anil compact, some- Characters,
times rather earthy.

Hardness, crystallic, sometimes only felsparic.
Fracture, conchoidal. Fragments, angular sharp.

Weight, sometimes siderose, sometimes grani-
tose.

Lustre, glistening, rising to shining, but some*
times dull. Opake; sometimes translucent on
the edges, but it then passes to jaspagate.

The most frequent colour of jasper is the red,
which has been found to contain from 16 to 20

* From the additions to Mr. Jameson's Mineralogy, ii. 603.

H 2



DOMAIN I. SIDEROUS.



of iron, and often attracts the magnet. It is
surprising that analyses have not been made of
a substance regarded as valuable.

Basanitc. Basanite, or the Lydian stone, is by many
regarded as a black jasper, seemingly with rea-
son, for its geognostic relations in veins, &c.
resemble those of the otker jaspers, and small
veins of quartz often traverse both kinds.
white jasper. The existence of white jasper has recently
been granted; but even this colour does not
refuse the presence of abundant iron, as may be
observed in the white ore of iron called steel ore,
or the spary iron ore, which is found to contain
from 30 to 40 of iron, with more than 20 of
manganese.

The black being admitted, jasper maybe said
to present all colours, except blue, which seems
however to occur in New Spain, or at least a
green approaching nearly to blue. The sinople,
or red jasper of Hungary, sometimes contains
gold*; and is said by Born to hold 18 of iron.
When Mr. Kirwan argues against this, from
the comparative lightness, he forgets that many
ochres, and even ores of iron, are comparatively
light ; nor is that metal itself of great specific



* The sinople of Heralds is green ! The earth of Sinope (see
Pliny) was red.



MODE XT. JASPER.



gravity, being much inferior even to tin or
copper.

" Mountains of striped jasper occur in Siberia, site?.
and often with breccias, but without petrifac-
tions, per Herman. 1 Berg. Jour. 1791, p. 84
and 94 ; of red jasper, ibid. 88 ; and also of
green jasper, 2 Gmelin. 81. (French.) It often
forms thick strata in mountains of schistose mica
in the Apennines, Ferber, Italy, 109; and in
Siberia, 2 Herm. 281. In Saxony it is found
alternating with, and sometimes mixed with,
compact red iron-stone, 2 Berg. Jour. 1788.
485.

* c In the south of France it occurs, reposing
on granite, and underlaying basalt, 3 Soulavie.
72. In the Altaischan Mountains it has never
been found in contact with granite, but it some-
times underlays argillite. 6 Nev. Nord. Beytr.
115."*

At Salisbury Crags, near Edinburgh, a curious
jasper, spotted with metallic iron, occurs under
the basalt. Saussure and Dolomieu have ob-
served that jasper is chiefly of an argillaceous
nature, more or less penetrated with oxyd of
iron. Patrin has given an interesting account
of the mountains of jasper in Siberia f, where he of Siberia.

* Kirwan, G. E. 177. t ii. 266.



102 DOMAIN I. SIDEROUS.

conceives that what he calls petrosilex passes
into jasper, by the influence of the atmosphere;
but in this he judges from the colours, and not
from the analysis. His primitive petrosilex, as
he declares, is felsite, while he places jasper,
which he calls primitive, after his secondary pe-
trosilex, which he expressly mentions is the
hornstein of Werner. There is therefore great
confusion in his context, as he derives a primary
rock from a secondary substance ; and his pe-
trosilex must be itself regarded as a dull and
imperfect jasper; nor is it inconceivable that
the surface may even attract more iron from the
atmosphere, where atoms of that substance con-
stantly float, as has appeared from many experi-
ments and inferences. The most beautiful jas-
pers of Siberia appear on the eastern side of the
southern part of the Uralian chain, particularly
the ribbon jasper, green and red, and that spot-
ted with pitchstone, or perhaps brown jasper.
Another beautiful kind presents, on a bright red
base, little undulating veins of olive green, ac-
companied by a white thread which follows all
the undulations. In Daouria, on the left bank
of the river Argun, one of the sources of the
Amur, there is a famous mountain composed of
green jasper; but, like the other kinds, it will
not rise in large pieces, but splits into small frag-



MODE XI. JASPER*

jnents. He observes that jasper is generally
schistose. A late traveller has informed us that
mountains of jasper extend for perhaps more
than a thousand miles through the eastern part
of Siberia, including Gore Island, between that
country and North America. On the contrary
the grand chains of European mountains seldom
or never present this substance; which is chiefly
found in Sicily, Bohemia, and Saxony.

It must be observed that many of the jaspers
rather belong to lithoJogy or gemmology, being
only found in geods or small veins. Nor is it
intended to be affirmed that they all belong to
the siderous domain, though the black, the red,
and the green, which are found in the greatest
abundance, appear always to belong to that di-
vision ; and it may be observed that these co-
lours also occur in basal tin, like which also jas-
per occurs in columns at Dunbar, in Scotland.

STRUCTURE I. COMMON.

Aspect 1. Black jasper. It is doubtful whether
this substance, the basanite or Lydian stone of
Werner, form entire mountains, though Kirwan
seems rather to imply that it does : but the sili-
ceous schistus of Werner, which includes basanite,
is so vague an appellation as to convey no idea ;



104 DOMAIN I. SIDEROUS.

and the application of the term has embarrassed
even the most skilful mineralogists.

Black jasper, from Prague.

The same, from Leipsic.

The same, from Hainchen, near Freyberg, in
Saxony.

The same, from the Pentland hills, near Edin-
burgh*.

Aspect 2. Red jasper, from Saxony.

The same, with granite adhering to both sides,
from the Spizleite, ^near Schneeberg.

Red jasper, or sinople, with grains of gold,
from Hungary.

The same, from Siberia, where it rises in moun-
tains f.

Aspect 3. Green jasper, from Daouria, where
it composes a mountain.

Aspect 4. Striped jasper. In green and red
stripes, from Siberia, where it forms a chain of
mountains.

* Brongniart, 1. 327, regards the siliceous schistus of Werner as
a schistose jasper He might rather, with Faujas, have called it
black jasper, most jaspers being schistose. As iron forms the
dominant principle of jasper, and black is the most usual colour of
its compounds, it would be absurd to reject black jasper.

f German and Dutch travellers sometimes call red jasper coraL



MODE XII. SLATE. 105

Brown jasper, it is believed, may also form
mountains or rocks ; but the other kinds, as the
Egyptian, the jaspagate, Sac. are only found in
small pieces, commonly globular.



STRUCTURE II. COLUMNAR.

This structure is very rare, and scarcely occurs
except at D unbar, in the south of Scotland, where
the interstices of the pillars are filled with sili-
ceous cement.



MODE XII. SLATE.

Texture, eminently schistose or slaty, com- Characters.
monly straight, sometimes curved or undulating,
of a very fine or impalpable grain.

Hardness, from marmoric to basaltic. Frag-
ments, sharp, splintery, sometimes rhomboidal.

Weight, granitose.

Lustre, sometimes dull, sometimes silky.
Opake.

The colour is most generally bluish, but some-
times greenish, or a purple red; also yellowish,
and sometimes with stripes or spots of a darker
colour. It is the thonschiefer, or clay-slate, of Names.
Werner, the argillaceous schistus of many English



106 DOMAIN I. SIDEKOUS.

and French mineralogists, being by all ranked as
a primitive rock. As it has been found to con-
tain from 14 to 20 of iron, it strictly belongs to
this domain, the clay being a very inferior con-
sideration. It has also a metallic appearance
and sound, very different from schistose clay or
clay-slate, strictly to be so denominated. The
simple term SLATE, besides the advantage of
being in general use, has been thought sufficient
to discriminate it by way of eminence. It ge-
nerally contains a portion of magnesia j and
when this is abundant, as appears to be indi-
cated in those kinds which have a very silky or
satiny appearance, it may be ranked among
the magnesian rocks. It often presents pyrites,
either in a cubic or dundritic form, sometimes
schorl, and even garnet and siderite. Actinote
also appears ; and a recent disco very chiastolite,
or hollow spar. Scales of mica often occur, as
in many other substances; nay it sometimes
passes into mica-slate : and Daubuisson has de-
monstrated, by an operose chemical analysis,
that they may be regarded as different modes of
the same ingredients.

It often forms entire mountains, but com-
monly only a part, alternating with gneiss and
mica-slate : nay, according to Kirwan and Pal-
las, both granite and gneiss often rest upon slate.



MODE XII. SLATE.



107



Sometimes veins of granite are found to pass
through this substance, which must not be ac-
cepted as only appearing in the finer form used
for slates, but also in coarse and thick schisti,
and sometimes, though rarely, even massive.

It is doubtful whether the yellow argillaceous
schistus, which composes the famous mountain
of Potosi, belongs to this description; as (the Potosi.
argillaceous schistus, or the clay-slate of n\any
other countries, so remarkably metalliferous,
cannot be classed under this division; which'
further evinces the utility, if not necessity, : of a
far greater abundance of definitive denominations
in this new science. But Helms seems to con-
sider the Andes as chiefly composed of what
Ki r wan calls primeval blue argillite ; and he de-
scribes the yellow slate of Potosi as being ex-
tremely hard. If they contain frorp J/J to 20 of
iron, they belong to this divisio* '; and as iron
commonly accompanies the richest ores, it is
probable that its presence is here indicated.
But Humboldt regards that amazing chain of
mountains as chiefly composed of what is called
argillaceous porphyry; while those of New Spain
are of argillaceous schistus: roofing-slate, and
its correlatives, being regarded as rare.

There are valuable quarries of slate in Corn- Quarries,
wall, Wales, Westmoreland, and Scotland. A



]08 DOMAIN I. SIDEROUS.

curious account of the manner of working those
of France, near Angers, may be found in the
Journal des Mines.

In his account of the primitive schisti, Patrin
has the following article*:

Slate of Ural. " Ferruginous schist u-s. This slate is mostly
composed of hardened clay, abundantly mingled
with an oxyd of iron, either black or brown,
so^ stimes red or yellow; a little quartz; and
i> 'h mica. This rock is one of the most com-
mon in the northern countries, where iron is
singularly abundant. The eastern part of the
Uralian chain of mountains, for an extent of
about 500 leagues from north to south, is almost
entirely composed of this rock."

The same able author gives the following ac-
count of. the slate-mines at Charleville on the
Meuse, w-Jiich he regards as primitive ; and
afterwards of Jiose of Angers, considered by
him as secondary.

" The slate-mines of Charleville are not ex-
plored by open quarries, like those of secondary
slate, but by subterranean galleries, because the
roof of the bed of slate is composed of banks
of quartzose schistus, very hard and very thick;
and besides, the slate plunges very rapidly under

* i. 120.






MODE XII. SLATE. 109

this rock, which would render enormous clear-
ages necessary, and would expose the workmen
to great danger from falls of the rock.

" The principal slate-mine of this country is
that of Rimogne, four leagues to the west of
Charleville. It is in a hill, of which the centre
is primitive, but the skirts are in part covered
with beds containing shells. The mouth of the
mine is towards the summit; the bed explored
inclines forty degrees to the horizon, so that to
advance four feet, you must descend about three
feet perpendicular. The workmen call this bed
the plate, on account of its form, which is flat
and thin, if the extent be considered. Its thick-
ness is nevertheless sixty feet; but its length and
breadth are incomparably greater, and their li-
mits remain unknown. It has been pursued, by
a principal gallery, to the depth of 400 feet ;
and they have driven many lateral galleries,
which are prolonged about two hundred feet,
on each side of the main gallery; where are
placed, in succession, twenty-six ladders, for the
passage of the workmen, and the carriage of the
slate.

" But in this thickness of 60 feet, there are
only 40 of good slate : the remaining 20 of the
underpart are full of quartz, and unmanageable.
The rock, which forms the immediate roof of the



110 DOMAIN I. SIDEROVS.

slate bed, is a granular quartzose schistus, called
grit by the workmen ; while the other upper
beds are of a friable clay-slate, of an iron colour.

" This bed of slate is the most considerable
known in the country, and I doubt if any similar
be found elsewhere. The slate resembles that
of Angers, in its quality, and its deep blue co-
lour.

" That of the other quarries in the environs
of Charleville is subject to be mingled with py-
rites, and intersected in all directions by veins
of quartz, which are called cordons. The slates
of some mines are greenish, like those of certain
quarries in the Pyrenees.

" In order to quarry these slates they cut out
blocks about 200 pounds in weight, which are
called Jaijr. Every workman in his turn carries
them on his back to the very mouth of the pit,
mounting with infinite labour the twenty-six
ladders of the great gallery, or at least a part, ac-
cording to the depth of the bed. When brought
to the working place, these blocks are first split
into thick tables, which are called repartons ;
this operation is easy: the workman holds the
block between his legs, puts a chissel any where
to the side, and divides it with the blow of a
mallet. The repartons are treated in the same
way ; he only takes care when they become too



MODE XII. SLATfi.



Ill



thin, to break them in two, by their breadth, in
order to prevent their fracture. These operations
must be performed soon after the blocks are
drawn from the quarry ; for if the stone has time
to dry, it would no longer be possible to split it.

" The engineer Vialet, who has given a me-
moir on this slate-mine, says he found a mean
of giving these slates double their natural hard-
ness, which was by baking them in a brick-kiln,
till they had assumed a red colour. In this case
they are not more brittle than before; but as
they acquire great hardness by this process, as
indeed any argillaceous substances will do, they
ought to be formed and pierced before they are
put into the oven.

" It is surprising that the slate of Rimogne
presents no vestige of marine bodies, while the
neighbouring lands are full of them; but this
surprise will cease, when it is observed that na-
ture has formed the different portions at epochs,
and under circumstances, widely different/**

Nor is his account of the slate quarries of An-
gers less interesting, which he places among the
secondary, and regards as far more rare than the
primitive.

" France possesses many of these large beds



*



Patrin Miii. iii.



] 12 DOMAIN I. S1DEROUS.

of slate, chiefly near Laferriere in Normandy,
and in the neighbourhood of Angers. The last
is the most important 5 it furnishes slate of the
most perfect quality; and its extent and pro-
digious thickness make it be regarded as in-
exhaustible.

<c This bed extends for a space of two leagues,
from Avrille to Trelaze, passing under Angers,
where the Mayenne, which comes from the
north, cuts it at right angles.

" The town of Angers is not only covered but
built with slate, those blocks being employed in
masonry which are the least divisible.

" The quarries which are actually explored
are all in the same line, from west to east, as
well as the ancient pits; it being in this di-
rection that, by the exterior disposition of the
soil, the bed of slate presents itself nearest the
surface. Immediately under the vegetable earth
is found a brittle kind of slate, which, for four
or five feet in depth, splits into little fragments
of some inches, which have the form of a rhom-
boid, or a portion of that figure.

" A little lower is found what they call build-
ing stone, being a pretty firm slate, but scarcely
divisible into leaves. This is employed in the
construction of houses, after it has been suffi-
ciently hardened by being dried in the open air*



MODE XII. SLATE. J J <}

" At fourteen or fifteen feet from the surface
is found the good slate^ which has been quarried
to the perpendicular depth of about 300 feet,
the remaining thickness being unknown.

cc The operations are conducted by open quar-
ries, by successive foncees, trenches, of about
nine feet deep, gradually narrowed, in order to
preserve a slope sufficient to prevent lapses of
the rock; so that a trench, four hundred feet in
width at the opening of the quarry, shall be re-
duced to nothing at the thirtieth jftwaV, that is
the depth of 270 feet. There is every reason to
presume that a far greater depth might be at-
tained, and with more advantage, as the lower
they have gone the more perfect is the slate.
They have only been stopped by the difficulties
presented by the method pf quarrying hitherto
adopted, which appears not to have been the
best, in one respect particularly, which is, that
the quantity of slate diminishes as the quality
becomes better, so that in the total mass those
of a middling quality are far more numerous.
It would seem that the method of subterranean
galleries would prevent the inconveniencies of
the present plan ; there would not at least be
lost and overwhelmed a prodigious quantity of
excellent slate. The slate-mines of Charleville
might serve as an example; where, in spite of

VOL. I. I



DOMAIN i.



the disadvantageous situation of the bed, which
renders it more difficult to be worked than if it
were horizontal, the product amply repays the
undertakers, though the galleries be of great
length, and some even pass under the river
Meuse. Slate is far more valuable than coal 5
and yet all mines of the latter are explored by
pits and galleries, sometimes of immense depth :
those of Charleroi, in the Netherlands, are about
two thousand four hundred feet in perpendicular
depth j those of Whitehaven, in England, about
five thousand, while they extend more than half
a league under the sea. But works conducted
with skill overcome the difficulties which are
produced by these subterraneous excavations,
which are repaid with great profit, and no part
of the mineral treasure is lost. It would there-
fore be of great consequence to try if the method
of galleries could not be adopted at Angers.

" As to the interior structure of this great



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