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mass of slate, it is divided by many veins of cal-
careous spar and quartz, about two feet thick,
by fifteen or sixteen in height $ they are parallel
amongst themselves, and proceed regularly from
west to east, in a situation which approaches
the vertical, as they only decline seventy de-
grees towards the south. These veins are met
at intervals by similar veins, whose direction i$



the same ; and of which the inclination is also
seventy degrees, but in an opposite sense, so that
when they meet the former they either form
rhombs, or half rhombs, which Guettard com-
pares to the letter V; some being upright, while
others are reversed.

" All the layers or leaves of the slate have a
direction and inclination similar to those of the
first veins of quartz ; that is to say, that they
rise seventy degrees towards the south, and dip
towards the north : and even when intersected
by veins which have an opposite inclination,
theirs is not changed. The whole mass is thus
divided into immense rhomboids, composed of
plates all parallel amongst themselves, an.d with
the two opposite faces of the rhomboid.

" The slate of Angers is extracted in blocks
of a fixed size, which are divided, as at Charle-
ville, into rcpartons and leaves. It is betwixt
these leaves that there are frequently found ves-
tiges of marine animals, and above all pyritous
impressions of potts- de-mer (the sea-louse, a little
univalve shell of the courie kind) ; of little che~
vrettes (shrimps or prawns) ; and a kind of crab,
of which the body is about a foot in breadth,
and fourteen or fifteen inches in length, the tail
having nine OF ten rings. The shrimps are
sometimes so numerous, that Guettard counted



forty upon a slate of only one foot square. But
it must be observed that none of the above ani-
mals have similar representatives in living zoolo-
gy. But what appears most surprising in these
impressions, particularly with regard to the large
crabs, is, that the body, though there be no sign
of its being crushed, may be said to have no
thickness whatever. They are rather simple
engravings than bodies in relievo, the convexity
of these large crabs upon a thin leaf of slate not
exceeding the quarter, or even the tenth part, of
a line; nor is it perceivable that the body of the
animal at all penetrates the thickness of the leaf
where it is adherent. And what still adds to
this wonder, is the nearly vertical situation in
which these impressions are found in the mine.
" A series of leaves of slate may be compared
to a set of books placed upon shelves ; and the
impressions of crabs and other animals, to en-
graved plates in the volumes. They do not, in
fact, occupy more thickness ; and it is equally
difficult to conceive how the body of these ani-
mals, though otherwise perfectly defined, should
be reduced to a simple surface without thick-
ness : and how it should always be found in a
vertical situation, which cannot be ascribed to
any derangement in the bed itself, since it is
still horizontal, and occupies a space of many


leagues. The difficulty of supplying such phe-
nomena has led some to imagine a plastic force
in nature, a power of modelling, in the mineral
kingdom, forms analogous to those of organised

" These slates also often present beautiful py-
rites in the form of trees, more than a foot in
extent, which are regarded by Guettard as im-
pressions of tremelltf. The pyrites is sometimes
in small grains, disseminated like a dust upon
the surface of the slates ; where may also be ob-
served many little stars of selenite.

" When the blocks have been drawn from the
quarry, if they be left exposed to the sun or to
the open air for some days, they lose what is
called the quarry -water, become hard and un-
tractable, so that they can only be employed in
building. Frost produces a singular effect on
these blocks : while frozen they may be divided
with more ease than before; but if thawed a
little quickly, they are no longer divisible. Yet
this quality may be restored by exposing them
once more to frost; but if the alternative be
often repeated, it becomes impossible to reduce
them to leaves.

cc The secondary slate which is found in other
countries, offers nearly the same dispositions and


phenomena as that of Angers. It is a substance
as rare in other countries as in France, there
being only one or two quarries in England, in
the county of Caernarvon. Switzerland presenti
no slate, except in the valley of Sernst, in the
canton of GJaris.

'* Italy has only one slate-quarry, that of La-
vagna, in the state of Genoa, which furnishes a
slate of an excellent quality, and so impene-
trable to fluids, that it serves to line the cisterns
in which olive-oil is preserved.

** Germany presents many kinds of secondary
slate (clay-slate), containing impressions of rep-
tiles, fish, and other animals ; but these impres-
sions have a considerable relievo, and it is evi-
dent that the animal has existed. The most
remarkable of these slate-quarries are those of
Eisleben, in Saxony; of Ilmenau; of MansfeJd,
in Thuringia ; and of Pappenheim, in Franconia.
I have often seen, in the mountains of Siberia,
beds of primitive slate, more or less considerable;
but they are mostly aluminous, and furnish the
kamennoie maslo, or rock butter, a fat yellowish
substance of a penetrating smell, being a mix-
ture of alum and fluid bitumen. But I have no
knowledge that in all this immense country there
is one bed of secondary slate. Nor does Bowles,


in his Natural History of Spain, indicate that
lie has observed any in that kingdom*.*'

To these accounts may be subjoined a short
description of a remarkable quarry in Cornwall,
unknown to Patrin.

" Between Liskeard and the Tamar, on the
south-west, are some quarries of slate, which
supply the inhabitants of Plymouth with cover-
ing for their houses, and for the purpose of
exportation. Several quarries have also been
opened at other places; but the best covering-
slate in Cornwall, or perhaps in England, is pro-
cured at Denyball, nearly two miles south of
Tintagel, in the north part of the county. The
whole quarry is about 300 yards long, 100
broad, and almost 40 fathoms in depth. The
slate-rock is disposed in strata, dipping to the
south-west, and preserving that inclination from
top to bottom. It is first met with at about
three feet below the surface of the ground, in a
loose, shattery state, with short and frequent
fissures ; the laminae of unequal thickness, but
not horizontal. Thus it continues to the depth
of ten or twelve fathoms, when a more firm and
useful stone is procured, the largest pieces of
which are used for flat pavements. This is called

* Patrin Mi. iii, 307-



the top-stone, and continues for ten fathoms;
after which the quality improves with the in-
creasing depth a till, at the twenty- fourth fathom
from the surface, the workmen arrive at the
most superior kind, called the bottom-stone.
The colour is grey blue ; and the texture is so
close, that it will sound like a piece of metal.
The masses are separated from the rock by
wedges, driven by sledges of iron, and contain
from five to fourteen superficial square feet of

" As soon as this mass is freed by one man,
another stone-cutter, with a strong wide chisel
and mallet, is ready to cleave it to its proper
thinness, which is usually about one eighth of
an inch : the pieces are generally from a foot
square to two feet long, by one wide ; but the
flakes are sometimes large enough for tables
and tomb-stones*."


Aspect 1. Ash grey slate, from Angers, in

Bluish grey slate, from Westmorland.
Purple or reddish purple slate, from Anglesea,
The same, with pyrites, &c.

* Brayley's Beauties of England, ii. 32Q.


Aspect 2. Killas, from Cornwall, many va-
rieties ; blue, grey, or whitish yellow. If it con-
tain only 6 of iron, it belongs to the argillaceous
or to the magnesian schisti.


The same identic substance of which slate is
composed has been discovered in France, and
other countries, in a massive form, or stratified
with the seams at great distances, and incapable
of being split into thin plates, like common slate.
It may probably be often discovered in the vicinity
of slate-quarries.

The slate with impressions so frequently found
with coal, and called shale, is commonly of an
earthy texture, and belongs to clay-slate.

Saussure mentions slate in columns like basalt*.
He also enumerates the following :

598. Granite, joined with slate; the last being
composed of mica and pierre de come.

1862. A slate, with mica, in leaves thinner
than paper, sometimes straight, sometimes undu-
lated. It is, according to Saussure, a mixture of
ferruginous clay and mica.

* i. p. 523, 4to.


2 1 22. On the passage of Simplon an inter-
mediate slate, between the mica and the common,
of a brilliant and undulated appearance, contain-
ing garnets.


Arrangement. It is difficult properly to arrange mica slate.
Though it contain a great quantity of quartz, it
has always been classed among the argillaceous
substances, as the mica is the chief character-
istic. Mica sometimes contains no magnesia;
but according to the analyses given by Haiiy,
the brown, grey, or black, which are the most
abundant and common in mica slate, contain a
greater portion of iron than of argil, the quan-
tity of potash being also considerable. Bergman
found 9 parts of iron in mica ; Kirwan nearly
20 : even of the colourless kind Klaproth dis-
covered 15 in one sort, and 22 in another.

Connexions. Mica slate has also a natural connexion with
common slate, into which it often passes*. It
must also be observed that Saussure found in the

* Daubuisson's curious and elaborate analysis (Jour, de Ph.
180Q) proves, that the composition of mica slate and slate is identi-
cally the same. The made fprms J&e only difference.


Alps rocks in which scales of iron supplied the
place of mica. In all events the black mica
must belong to the siderous division ; while the
white mica, which might be called micarel, and
sometimes passes into steatite, ought to be classed
among the magnesian substances*.

Mica slate has a further affinity with the si-
derous substances, as, like siderite, it frequently
contains garnets. It is very metalliferous, many
of the mines of Norway and Sweden, and a part
of those of Saxony and Hungary, being situated
in this rock.


Mica slate of a jet black, with black quartz,
from Switzerland.

Grey mica slate from Scotland, where it abounds
in the Grampian Mountains and some of the isles;
not to mention innumerable other regions.

Grey mica slate, used for ovens (Stellstein),
from Sweden. Wall. i. 427.

* Kinvan has called the brownish black mica micwelle, be*
cause it contains no magnesia ! KlaprQth found in it :
0063 argil
2g5 silex
675 iron



In very thin plates, and - of an almost impal-
pable grain, from Scotland.

Brown mica slate, from the same countries.
The green and white need not be here specified.


The noted kornberg of the Swedes belongs to
this division, being a coarse mica slate irregularly
contorted. It is very metalliferous *. As it is a
celebrated rock with a barbarous appellation, it
may be called Linnite, in honour of Linnaeus, a
native of Sweden, who however contributed but
little to its mineralogy.

Linnite, from Sweden.

The same, from Norway.


\Vhen mica slate is mingled with garnets, it
constitutes the Murkstein, or Norka, of the Swedes,
and the latter name might be retained, if requisite;
but garnets form so common an adjunct of mica
slate, that the distinction seems unnecessary.

Mica slate, with garnets, from innumerable

* See Journal des Mines, No. 88, p. 257. It is granular, black-
ish, with thick and short layers.


The same, with schorl, from the Grampians.

The same, with sappare, the kyanite of Wer-
ner, from the mainland of Shetland, and from

The same, with various ores.

Saussure mentions the following varieties :

A rock of reddish mica slate, of which the
leaves, being often curved, present at intervals
quartz in the form of lentiles, but often some
inches in length, and one or two in thickness.

A remarkable mica slate, composed of thin
white and grey leaves, so as to appear on the
sides like a striped stuff; the grey part being
mica, and the white a very fine arenaceous quartz.

A gneiss, composed of jad and siderite ; his jad
being probably compact felspar. 1331.

A part of the chain of Mont Blanc consists of a
hard ferruginous quartz, mixed with mica. 847.

* Sappare is the ancient Scotish name, retained by Saussure, who _
informs us that he first received the substance from the duke of
Gordon. Werner's alteration is alike useless and absurd, the ori-
ginal appellation implying its similarity to sapphire, for which it
has sometimes been substituted by jewellers.



These rocks are far from being uncommon
among primitive mountains, being chiefly com-
posed of magnesia and oxyd of iron. In the
Chlorite and substance called chlorite by Werner, from its


green colour, the iron often exceeds forty parts
in the hundred ; and it is even used as an ore of
that metal. Of actinote*, by some called acty-
nolite, some kinds contain as much iron as is
found in siderite - 9 and it is in general considered
as only a different structure of that rock. Saus-
sure indeed regarded chlorite as only a kind of
earthy siderite; but as it contains a far greater
portion of magnesia than siderite, in which that
substance is scarcely recognisable, it seems more
proper to allot to these rocks an article apart :
and the chemical mode of combination is at least
very different.

To this Mode may also be added another
m i x ^ ure of iron and magnesia, those serpentines
which contain so great a portion of iron as to
affect the magnet. Most of the siderous rocks
consist of iron and clay. The eisenkesel, that is

* From the Greek OMfMtOS, radiated, so that the y is foreign to
the orthography.


the iron-flint, of Werner, is merely a vein-stone,
and never appears in the shape of a rock ; and
generally the silex in siderous substances is lost
in the argil. The sidero-calcite and ferri-calcite
of Kirwan have little connexion with the present
subject, the former being pearl-spar, the latter
only embracing a few lime-stones, which contain
from 10 to 20 of iron ; but as they easily decom-
pose, present no remarkable variety, and are
little interesting, it is unnecessary to distinguish
them, except as mere diversities of lime-stone.
Innumerable marbles are tinged with iron, from
which they chiefly derive their colours ; but it
would be a too nice and useless distinction to
compose an arrangement from this mere acci-
dence, which varies in different parts of the
same rock. There remain therefore only the
magnesian rocks to be specially considered in
their conjunction with iron, a metal with which
they have often a singular affinity.


This substance is by Werner divided into four
kinds ; chlorite earth, common or compact chlo-*
rite, foliated chlorite, and chlorite slata It seems
unknown to Wallerius, who published his last
editioft m 1772; but is the green talc of Born,


and the Samnterd of old German writers, perhaps
from its velvety appearance. To the Cornish
miners, as it often occurs with tin, it is also known
by the name of peach*.

The first Aspect, that of chlorite earth, can
scarcely be said to form a rock, chiefly occurring
in clay-slate, and probably forming the green no-
dules in basaltin. The second kind is perhaps
unknown, save as a vein-stone ; and what is called
the foliated is generally crystallised, being found
at St. Gothard with other crystals. The only
rock therefore of the kind is :

Aspect 1. Chlorite slate. Texture, finely gra-
nulated, sometimes regularly, sometimes irregu-
larly ; schistose, so that fragments sometimes as-
sume the form of a wedge.

Hardness, gypsic. Fracture, sometimes even,
or undulating, or scaly. Fragments, slaty, blunt,
except when mixed with quartz.

Weight, sometimes granitose > sometimes car-

Lustre, glistening, somewhat resinous. Opake.

Chlorite slate, from Egypt. Wad, 23, a small

Chlorite slate, from Corsica, Norway, Sweden,

* It is the laldogea of Saussure, so called from Monte Baldo.



Stiria, Tyrol, Scotland, &c. It is generally sprin-
kled with octaedral crystals of iron, and some-
times with garnets. The first are the most cha-
racteristic of this rock.

Chlorite slate, mixed with quartz. This kind
is commonly even schistose, but far more hard
than the former.

Saussure, 2264, expresses great surprise,
when, on receiving specimens of the chlorite slate
of Werner, he observed that there was scarcely
any chlorite in them ; and he adds, that the de-
nomination being quite deceitful, it ought to be

On the lofty summit called the Col du Geant,
Saussure found that the granite, like that which
is greatly elevated at Mont Blanc, can scarcely be
said to contain mica. Here its place was often
supplied by a small-grained chlorite* 1 .


This substance also chiefly occurs in small por-
tions. It is the strahlstein of the Germans, and is
by Werner divided into the asbestoid, the com-
mon, and the glassy. Of these it is believed the Glassy

* Sauss. 204.


last only appears in the form of rocks. Saussure,
who calls it delphinite, or green schorl of Dau-
phiny, describes a rock of this kind. He also
mentions smaller portions of a compact kind.

That the glassy actinote strictly belongs to the
siderous domain, will appear by the analysis of
Vauquelin; silex 37, argil 21, lime 15, oxyd of
iron 24, with a small portion of manganese*.

Texture, sometimes massive, but generally in
thin six-sided acicular crystals.

Hardness, between marmoric and basaltic.
Fracture, fibrous and radiated. Fragments, splin-
tery and very sharp.

Weight, siderose.

Lustre, shining and glassy; strongly translu-

Actinote, from Switzerland, where, as has been
mentioned, it forms entire rocks.


Of this kind Humboldt discovered a curious
rock with magnetic power, forming the mountain
of Regelberg, in Germany; the south side attract-

* Lametherie observes, that the earthy smell shows an approxi-
mation to hornblende. Th. de la Terre, ii. 373. Is not schorl a
black actinote?


ing the north pole, and the northern side the south

Rocks of the same kind may probably be dis-
covered in other countries ; at any rate many ser-
pentines are so replete with iron as to fall into
this division.

Saussure, 1342, gives a minute description of
what he calls granular serpentine. It is so much
impregnated with iron, that it belongs to the si-
deromagnesian rocks.

The mountain called Roth Horn is in a great
part composed of compact serpentine, semi-hard,
that is, of the hardness of marble. It is called
the Red Horn, because the serpentine, though
green within, is red on the surface, from the oxyd-
ation of the iron*.

* Sauss. 215?.

K 2



intrites. The rocks here called INTRITES, because crys-
tals or particles are imbedded in a paste, are
distinguished from Glutenites, in which the par-
ticles coalesce together with little or no visible
cement. The former have by the Germans
been styled porphyries, from a similarity of
structure ; but the interspersiori of a few crys-
tals, especially of felspar or felsite, substances as
common as mica, can hardly even be said to
alter the nature of the rock ; and such sub-
stances ought in geology to be classed with
their parent base; for while all these kinds of
pretended porphyries are classed under one head
by Werner and his disciples, great confusion
arises from their totally different natures.

In the present work the intrites and glutenites
are classed under the several domains to which
they belong; but as the bases are of different
kinds, it has been thought advisable to bring
them under one point of view, at the end of
each domain. As however the chief siderous
intrites are the genuine porphyries, the pre-
servation of that classical and universal name
will considerably restrict the present division.



When the crystals, instead of being of an oblong
cubic form, as in porphyries, assume an oval, but
particularly a round shape, the rock may be aptly
styled a variolite, every denomination being use-
ful which saves circumlocution.

The stones called variolites of Durance, being Variolites of


pebbles rolled down by that river in Dauphiny,
belong to this article*. The prominence of the
round crystals of felspar, having a faint resem-
blance to the pustules of the small-pox, has oc-
casioned this appellation. Patrin f has minutely
described the variolites of Durance, as being in his
eye the same with the ancient green porphyry,
being a corneenne, or basaltin, fusible into a black
amel attractable by the magnet. The |Ppts, of a
finer green, or sometimes white, are men sur-
rounded with two zones of these colours. Saus-
sure >lK whose description is very minute, J539,
regards the globules as composed of that kind of
felspar which, being of a greasy appearance, like
one of the kinds of quartz, is called unctuous fel-

* Faujas says that he found, near the village of Servieres, the
rocks which afford the variolites of Durance. For those of the
Drac, see Amygdalite.

f i. 147.


spar, or rather felsite ; for Werner has pronounced
that the felspar in the ancient porphyries is com-

The variolites of Turin are of a brownish grey,
of a shining and unctuous appearance, with spots
of a lighter grey, and white starry crystals. The
variolite of Sesia is of a reddish grey, with spots
of a bright brick red.

Saussure mentions, 1289, a kind of soft vari-
olite, seemingly composed of green siderite, with
spots of white felspar, sometimes rhomboidal,
sometimes circular.


Iron-stone, with crystals of quartz, from the
Surry hills.

Saussure mentions, 1322, a red and green
porphyry, or rather intrite, mixed with felspar
and actinote; the base being of granular felspar.



In arranging these substances, two objects oiutenitcs.
are to be considered; the nature of the frag-
ments or particles cemented, and that of the
cement itself. When they are both of one kind,
as a siliceous bricia*, or a pudding-stone with a
siliceous cement, there can arise no doubt con-
cerning their classification : but when, as often
happens, the fragments are of one kind, and the
cement of another, the domain may appear
doubtful. The more general method however
appears to have been, to denominate the sub-
stances from the cement, as being the pre-
dominating agent ; and this rule is particularly
applicable in the present instance, ajtoxyd of
iron forms the strongest of naturaWTements.
Bricias of basaltin or jasper are commonly ce-
mented by the same substance, and sometimes,
though rarely, by quartz ; but they may still be
referred to the predominating substance, the

1 This word is strictly Italian ; bricia, a crumb or small frag-
ment, with its derivatives Iricioletta, a little crumb, Iriciolino, and
Iriciolo. Breccia is only a corruption.

The Italian architects and statuaries gave the first modern classical
names to rocks, as granito, granitone, graniti?w, &c. &c.


quartz being common, and of inferior consi-
Rririasand The division of glutenitcs into bricias and

stones, pudding-stones, the former consisting of angular

fragments, the latter of round or oval pebbles,

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