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3 Earth-Slag.

CLASS V. Folcanic Rocks.
Pseudo Volcanic Rocks.

4 Columnar Clay Ironstone.

5 Polier, or Polishing Slate.

True Volcanic Rocks.

1 Ejected Stones and Ashes.

2 Different Kinds of Lava.

3 The Matter of muddy

4. Admission of Iron as an Earth.

The admission of iron, not as a metal, but as an earth,
may occasion some hesitation ; and a few preliminary obser-
vations become necessary. Many eminent mineralogists and Admitted by
, . , , A - , former authors,

geologists have led the way to this improvement, though

they have not formally introduced it into a system. It may
be preferable to adduce their testimonies in chronological

Linneus has thus expressed himself, in his brief and em- Linneus.
phatic language : " I have sedulously enquired, during my
various travels, into the production of stones, and have
learned that it is effected by precipitation and crystallisation ;
and that earths are deposited, while quartz, felspar, and mica
rise up. The female earths are impregnated by the male




salts, whence a more noble progeny j but many of the latter
are derived from Iron, a Proteus who changes according to

Influence of t ne disposition of each wife."* He thus insinuates his opi-
11 on. n i on O f the wide influence of iron, a metal which belongs to
all ages and formations ; and whose power is prodigious and
perpetual, even in animal and vegetable life. Bergman has
indeed asserted a similar wide diffusion of gold, which has
escaped the more recent and precise tests of chemistry, and
is now rather regarded as imaginary ; while the most nume-
rous and exact experiments more and more evince the uni-
versality of iron, which drops even from the atmosphere as
the chief ingredient of what are called meteoric stones, and
supplies volcanoes from the lowest abysses of the earth. Iron,
the grandest of the metals, is not only the most widely dif-
fused, but the most useful to mankind in all the stages of
society, and without it civilisation would be unknown j as it
furnishes the spade and the plough to the agricultor, tools to
the artisan, the compass to the mariner, armour and weapons
to the hero, and ink to the eternal theme of the author.
But waving these considerations, Linneus has thus sufficiently
expressed his opinion of its influence in the constitution of
rocks and stones.

Cronstedt. Cronstedt, who may be called the grandfather of modern
mineralogy, as Bergman is the father, had long ago a faint
discovery of this truth 5 for among his nine earths, several
of which have since been discarded, he reckons Garnet Earth,
which, as that substance is strongly impregnated with iron,

Bergman, can only be the siderous earth here mentioned. Bergman
also, in his Sciagraphia, which laid the foundations of modern
mineralogy, especially reckons the ferruginous among the six
principal earths, as he includes the barytic. In his account
of carbonate of lime, he mentions that it is seldom free from

* Lithogcnesiam studiose in itineribus qutesivi, dedicique earn absolvi Prge-
cipitatione et Crystallisatione ; atque Terras prosterni, sed Quartzum, Spatum,
Micamque, exsnrgere. Terras femineas dein impregnari a Salibus masculis,
indeque prognasci Nobiliores ; horum vero plurimos a Marte, Proteo magis
mutabili, pro indole cujuscunque conjugis. Linn, a Gmeliu, p. 4.


iron, which is found even in the most transparent, the calca-
reous spar of Iceland ; " and it may be said in general that
all minerals contain that metal."*

To these eminent testimonies may be added Kir wan, who Kirwan.
has nearly approached to this division ; for, after describing
the simple earths, he proceeds as follows :

t( Calces of Iron. To these simple earths we must also
annex the consideration of calces of iron, as they almost
always accompany earthy or stony substances, are mixed or
combined with them, and are the source of many both of
their external appearances and internal properties.

" Calces of iron are formed of iron, combined with dif-
ferent proportions of pure air, and frequently of water also,
and fixed air.

<f One hundred parts metallic iron are capable of taking
up 66 or 70 of pure air. When 10O parts iron contain but
40 of this air, the compound is still magnetic."f

In another place, after observing that any earth which
forms less than one twentieth of a compound, is seldom of
any importance, he proceeds to state that calces of iron in-
fluence in some measure the properties of a compound, even
when they do not exceed one thirty- third part of the whole,
that is, three in the hundred ; and if they be themselves
magnetic, they communicate that property to compounds of
which they form above one tenth J.

In a later production, and with more ample information,
he presents the following remarks. " The proportion of the ,

different materials contained in the chaotic fluid to each
other, may be supposed upon the whole nearly the same as
that which they at present bear to each other j the siliceous
earth being by far the most copious j next to that, the fer-

* 1792, i. 170. ii. 378.

f- Min. i. 17. Calces were powders, now called oxyds. Thomson, i. 132.

1 Ib. p. 48. In his treatise on the Magnet (Mem. R. I. A. vi.), Mr. Kir-
wan says that iron abounds in all minerals, from 2 to 25, but at a medium 6.
This globe, he adds, is 4.5 heavier than water; and, p. 182, thinks the centre
ironj and afterwards calls it a great magnet, in which Haiiy coincides,



ruginousj then the argillaceous and calcareous; lastly, the
magnesian, barytic, Scottish, and Jargonic, in the order in
which they are named ; the metallic substances (except iron)
most sparingly." After such illustrious authors, it is scarcely
necessary to mention the similar ideas of Lametherie*.
Dolomieu. In his celebrated memoir on rocks, Dolomieu observes that
they are chieHy composed of four principal earths, to which
may be joined iron, or the earth which produces it : and he
adds that, in this memoir, " he never considers iron under
the relation of its metallic properties, but as a simple earth,
susceptible of the same kinds of combination as the other
elementary earths."f In his theory, Dolomieu supposes that
the precipitation of the principal earths took place in the fol-
lowing order : the siliceous, the argillaceous, the magnesian ;
contemporary with which two last, was that of the ferru-
ginous, or, as it is here denominated from the Greek, side-
rous ; and last of all the calcareous J.

In the continuation of this memoir he considers the ag-
gregation of the five principal earths, estimated according to
its comparative force, to be in the following arrangement :
siliceous, argillaceous, ferruginous, calcareous, and magne-
sian. He remarks, as a singularity in the ferruginous earth,
that it often lends more hardness and solidity to masses
where it is simply mingled, than it can acquire when it is in
a state of purity. He afterwards proceeds to various observa-
tions on the force of adhesion of these five principal earths,
and gives a table to illustrate this quality.

Patrin. Patrin, who often looks upon nature with an original and

inquisitive eye, has introduced many illustrations of the ne-
cessity of the siderous division. Among the primitive schisti
he enumerates " Ferruginous Slate. This slate is chiefly
composed of indurated clay, abundantly mixed with Oxyd of
Iron, either black or brown, but sometimes yellow or red,

* Theorie de la Terre, Tome i. p. 435. Tome iv. p. 45, &c.
f- Journ. de Physique, Tome 39> for 1791, p- 374.
t Ib. 382.


with a little quartz, and a considerable portion of mica.
This rock is one of the most common in the northern coun-
tries, where iron is singularly abundant. The eastern side of
the Ural mountains, for an extent of about five hundred
leagues, from north to south, is almost entirely composed of
it." He afterwards observes, that in Siberia many moun-
tains are composed of trap or basalt, " containing masses or
veins of granite ; while the granitic mountains often contain
veins and masses of trap or hornblende."* This last obser-
vation may be universally extended -, and evinces that siderite,
and even trap or basaltin, is at least as ancient as granite,
which has hitherto been gratuitously admitted as the most
ancient of all the rocks. He also adds, that he has seen
large mountains of hornblende, or siderite, in the Altaian

In treating of iron, Patrin observes that the veins or beds
of iron ore, are constantly parallel to the beds of the rock,
which in the primitive mountains are often vertical, and
seem from the first to have formed an integral part of the
mountain which contains them 5 whence Buffon has called
them primordial mines - 7 whilst the veins of other metals
almost always intersect these beds under different angles,
sometimes even at right angles, and evidently appear to have
been of a formation posterior to that of the rock. He pro-
ceeds to observe that the mountain of Blagodat, on the
eastern side of the chain of Ural, consists of thick beds of
iron, separated by others of slate and a kind of trap. In
that of Keskanar, in the same quarter, the celebrated mag-
nets are mixed with a quantity of greenish siderite in small
spots, and extremely resplendent when the stone is polished.
In the Altaian chain, vertical beds of an ochry slate alternate
with compact beds of black iron ore. The primordial beds
are chiefly composed of black iron ore, often magnetic - y the
strongest magnets of Siberia being those which present la-
minar parts, sometimes of iron, sometimes of hornblende or

* Min. i. 120, 127. f Ib. 132.


serpentine. The nucleus of the earth, as he observes, must
be chiefly ferruginous, as is not only announced by the gene-
ral phenomena of magnetism, but by the observations and
experiments of Maskelyne and Cavendish, which show that
the specific weight doubles that of rock crystal*.

In his mineralogy, Patrin begins with a description of the
primitive rocks, which he introduces by that of the chief
substances of which they are composed, namely, quartz,
felspar, mica, and schorl. This last term is generally used
by the French geologists for siderite or hornblende. ' ' Often,"
says Patrin, " it forms considerable masses of rock, and
even entire mountains. When the schorl-rock presents a
distinct laminar texture, it is called hornblende ; when the
texture is of an earthy appearance, it is named Comeene."
This last word is often used by the French for basaltin.
Thus, in the opinion of this great observer, who has passed
many years in the mountains of Siberia, schorl or horn-
blende, composed of siderous earth, is as primitive as any of
the rocksf.

Magnetism. But while these great geologists admit the ferruginous or
siderous among the principal earths, they seem never to have
connected this idea with that of most writers on magnetism ;
who, in order to explain that phenomenon, are forced to
admit that the nucleus of this our planet is a mass of iron :
and as, according to all theories, the substance which is
nearest the centre must be the most ancient, of course the
siderous earth must often partake of this antiquity j and in-
stead of ranking it, with Dolomieu, in the third or fourth
succession, it may be more properly classed in the first. In
the mica of granite, and often in the felspar, and even in the
quartz, a portion of iron is discoverable : and basalt, which
contains a large portion Of iron, is sometimes intermixed

* Min. v. 11, 48, 241. The mountains of Stjlinga, he says, are chiefly of
hornschieffer and hornblende.

f* Siderite and schorl shoot across quartz and felspar, so are more ancient :
so siderite and basalt intersect granite.


with primeval granite*. In the other most ancient rocks,
particularly those of hornblende or siderite, iron also abounds j
as it does in jasper, common slate, trap, serpentine, and the
oldest sandstone.

It may be necessary, however, to introduce a distinction
between the Siderous Earth and metallic iron, which must
depend upon the proportion to be found in various substances.
As the alkaline earths, though they yield metals, will scarcely
by any mineralogist be classed among metallic substances' 5 so
Siderous Earth, though it yield iron, may be admitted among
the other principal substances of that class. In fact, as the Dr. Davys
recent discoveries of Dr. Davy evince that the alkaline earths, dlscoveries -
that is the calcareous, magnesian, barytic, strontianic, are of
a metallic nature or yield peculiar metals, while he suspects
the other earths to be in the like predicament (as the sili-
ceous has since proved), it would be absurd to reject iron as
an earth, merely because it yields a metal.

It has already been seen that the presence of this earth, Power of iron,
even in a small quantity, is so powerful as greatly to affect
the compound 3 and, by altering the quality of its mode,
even to change its substance and denomination. Among
many examples may be mentioned the hyalite of Dauphiny,
which only contains 10 of iron in 100, yet the form of the
crystals is that of the iron ore of Elba. Many mineral sub-
stances receive their denominations, not from the abundance,
but from the influence of particular earths ; for the greater
part of the argillaceous and talcous rocks contain two thirds
or three quarters of silexj so that if the abundance alone
were regarded, two of the chief denominations of the mi-
neral kingdom would be rejected. In many instances, the
energy of one ingredient has far more force than the abun-
dance of another. An able chemist, after discussing some Energy of
difficulties of this kind, thus proceeds : " These circum- in ^ redients '
stances no doubt arise from the modes of chemical analysis

* The granite of the Hartz even affects the Magnet. Jam, Min. Sc. Isles,
p, 65.


being yet imperfect ; and particularly from our being still
almost wholly ignorant of what determines the properties of
compounds so complicated as minerals generally are. All the
ingredients are not to be regarded as equally energetic, or as
in the same proportion contributing to the peculiar constitu-
tion of a compound $ and if one, which in its relation to
others is comparatively feeble in its action, be present in
large proportion, it leads to erroneous conclusions, when, in
determining composition, we attend merely to the relative
quantities of the principles, without attending to their rela-
tive energies. This has been generally hitherto done ; and
among the earthy fossils, the predominating principle has
always been regarded as that which is present in largest pro-
portion, though the reverse is probably frequently just."*

5. Miscellaneous Observations.

This introduction shall be closed with some miscellaneous
remarks, which may not be found unuseful for the previous
consideration of the reader.

The science A grand cause, as elsewhere observed, of the slow progress
too extensive. Q f m j ne ralogy, when compared with other parts of natural
history, is that it is too wide for the labours of one man ;
whence some important parts have remained uncultivated,
while others, often comparatively minute, have been discussed
with great care and anxiety, according to the peculiar studies
and inclinations of the several authors. The progress of
zoology and botany has been greatly assisted by the publica-
tion of detached works upon several divisions 3 and even the
mosses and lichens have been found sufficient for one man's
attention, in the brevity of human existence. Recent authors

* Murray's Chemistry, iii. 7 He had already said, p. 5, " each simple
earth giving its name to an Order, under which are arranged the fossils in
which it is predominant, or to which it gives a predominating character" And
so Bergman, the father of modern mineralogy, in the preface to his Sciagra-
phia, 1782 : "I have derived the genera from the dominant principle; and the
species from the diverse mixtures."


upon these two kingdoms have hence been enabled to glean

the most interesting topics, and to form general compilation*

of great merit and accuracy. For as vita brevis, ars longa,

was the axiom of Hippocrates, who compiled his classical pro-

ductions on medicine from cases preserved in the temples, so

in all the other sciences, the mere observations of one man

will not constitute a science or a system. Saussure passed

forty years amongst the Alps ; and if the years consumed by

other travellers and authors, whose works have been used in

the present compilation, were computed, they might amount

to a thousand j a period belonging to nature and science,

but not to man. Hence the utility of general systems or Utility of

compilations, which, by combining in one view the observa- comp^ations.

tions of practical or scientific predecessors, not only by colla-

tion and elision render them more intelligible, but ascertain *

the progress attained by any science - } so that future diligence

may not be wasted in the investigation of subjects already

illustrated, but be directed to such parts as remain unculti-

vated and obscure. In this also, as in the other sciences,

more genius is required to build a system, than to make

observations. In the latter, Newton must yield to Herschel.

As the study of mineralogy commenced upon principles petralogy dif-
afterwards found to be inadequate and erroneous ; so, by a
similar fatality, the study of rocks has been confounded with
what is called geology, or the doctrine of the constitution of
this globe, which rather belongs to natural philosophy.
Petralogy, like lithology, or metallogy, is a science which
must be studied by the geologist j but a theory of the earth
may as well be studied in a pebble, as in a rock ; and the
neglected plains, as being nearer the centre of the earth,
must afford more topics than the lofty rocks and the moun-
tains. There is ,no reason, therefore, particularly to connect
petralogy with geology, or what some call geognosy : and it
would be alike absurd and useless if a rock could not be
classed, without a dissertation to determine its antiquity.
Nor can any reason be perceived why Werner should regard


empirical characters as the chief in regard to the rocks,
while he justly considers them as the last and meanest in the
consideration of other mineral substances. Here, as in other
provinces of the mineral kingdom, there is no infallible
guide but Chemistry -, upon which alone a rational and dura-
ble system can be founded. And if, as some few suppose,
chemical operations lead us to educts instead of products,
the difference remains the same, and the distinctions equally

Futility of Yet some ingenious men, who have made a tour of a few
tours, hundred miles, aspire to the study of geology, and speak of
their observations with all the pride of ignorance, and all the
vaunts of enterprise ; while one simple perusal of Saussure's
work would teach them that they knew nothing. In the
momentary duration of human life, as man writes with his
hand on the table and his foot in the grave, infinitely more
knowledge must be acquired by the study of former authors,
than by trifling observations, which would probably not even
have been made if the fugitive traveller had previously studied
the subject, or had even once revisited the spot, as Ferrara
has observed of Dolomieu. While an author in his cabinet
studies the whole globe, and the collective labours of two
thousand years, these little journeys only impress him as
puerile excursions ; and, in conversation, he regrets to find
the smallest tourists the greatest boasters. Da Costa has
illustrated this truth by a ludicrous story : Dr. Meara, having
the greatest respect for his own abilities, and regarding his
own discoveries with much admiration, was travelling on
Landsdown near Bath, when he observed a kind of chalk, of
quite a new species if not genus, being of a white colour,
remarkably pure, but above all very hot in the mouth ; and
in consequence he wrote a dissertation to prove that this
chalk alone was the long investigated cause of the heat of the
Bath waters. This celebrated discovery has passed into the
last edition of the valuable mineralogy of Wallerius, who
even quotes Da Costa as his authority for this new chalk.



though that patient writer had only mentioned it, to inform
his readers that it was unslacked lime, which had fallen from
a broken cart.

Such tourists, while they have themselves seen as little as Study of rocks,
they have read, are as loud as Dr. Meara in their assertions
that rocks can only be studied in nature ; while, in fact, it is
as impossible to discern rocks from nature alone, as from
books alone. The one must assist the other. The vague-
ness of ideas in the works of Dolomieu and Faujas, and
many other observers, is such that nothing can be learned.
But how distinguish rocks, or acquire accurate knowledge, Necessity of
from works of which the authors cannot distinguish a granite ex ciauJre! 6 "
from a porphyry, &c. ? If, in zoology, a horse was called a
lion by one writer, a tiger by another, a leopard by a third,
and a panther by a fourth, what knowledge could be acquired ?
or if, in botany, the rose of one author was the lily of an-
other, while others styled it by a hundred different names ?
While Buffon and his disciples speak with contempt of nomen-
clature, they might as well tell us that in civil history the
actions of Pompey might be ascribed to Caesar, and those of
Anthony to Cleopatra, for of what consequence are names ?
Saussure, with his usual judgement, pursued a very different
course ; and the most laborious parts of his work are evi-
dently those in which he attempts to establish a precise
nomenclature. It may safely be asserted that the science can
have no foundation till a precise and rich nomenclature be
established 5 and that till then it will remain a chaos, and
not a world.

The student of rocks must therefore begin with a precise
nomenclature, as otherwise his observations cannot be of the
smallest utility. If he mean to pursue this study, he may
also find it more interesting to pass from this arid subject
to the beauties of crystallisation and the metals ; and thus
from great and general ideas descend to minute. The
student of zoology would scarcely begin with entomology.
But even among the authors of mineralogy there are ore and
dross : and who would beliere that an hundred authors have


fallen into the grossest errors concerning ophite, &c. because
they neglected to consult the original passages?

In the present work, it is hoped that the want of attention,
care, or labour, will not be accused. The author has sedu-
lously employed the intervals of ten years in this production,
particularly three which he passed at Paris, where he had
constant opportunities of seeing the most opulent cabinets,
and of conversing with men eminent in the science, as
Patrin, Gillet Laumont, Daubuisson, and others j not to men-
tion interviews with Haiiy, and with Werner during his short
stay in that capital. It was resumed at intervals of other
studies, the change of labour being itself an amusement.
He hopes the work may at least aspire to the humble praise
of utility, the chief aim of his labours : terar dum prosim.
In the preface to his grand treasure of ancient knowledge,
Pliny has observed that it is laudable to mention the authors
by whose works ycu profit. Not contented with exact refer-
ences, the author has often adduced the original passages,
not only for the sake of greater accuracy, but to save the
reader the trouble and expense of consulting many works,
which perhaps contain only a few pages on this particular
subject, which has hitherto been treated as a mere appendage
to mineralogy. There are also numerous extracts of great
value, from works in foreign languages, of which, from
their nature, the English reader can scarcely ever expect to
see complete translations. These extracts will, it is hoped,
from the variety of the style, throw some flowers over a sub-
ject proverbially barren 5 while the expressions of the ob-
servers themselves, in the sensations arising from grand phe-
nomena, sometimes enliven the subject with somewhat of a
dramatic interest. It must also be remembered, that mosaic
is even more difficult than painting, and of incomparably

Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 4 of 35)