John Pinkerton.

Petralogy. A treatise on rocks (Volume 1) online

. (page 16 of 35)
Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 16 of 35)
Font size
QR-code for this ebook

A gneiss, composed of grey felsite and grey
mica. 1877.

1 A gneiss of foliaceous mica, with plates of
quartz, sometimes mixed with felspar, forms the


mountain which contains the copper mines of St.
George. 1201.

Werner has a large piece of massive granite,
inclosing rolled pebbles of gneiss. 2143. Saus-
sure gives, 661, examples of granite imbedded
in mica slate, or rather gneiss.

In the mountains on the south-east of the valley
of Chamouni, the inferior parts are gneiss, while
the summits are granite. 677.

Mount Rosa is wholly composed of veined gra-
nite, gneiss, and schistose rocks, from the base to
the highest summits. 2 1 38.


Characters. Texture, impalpably fine, resinous.

Hardness, basaltic, sometimes felsparic. Frac-
ture, conchoidal; if impure, splintery or coarse-
grained. Fragments, irregular and sharp.

Weight, carbonose.

Lustre, from glistening to splendent, resinous.
Somewhat translucent; but the black only on
the edges.

The colours are various shades of black, and
sometimes grey, brown, red, seldom green ; but
the tints are commonly pale.
site*. Pitch-stone forms entire mountains in Mis-


nia ; and in other mountains of that country it
forms large strata, that alternate with porphyry*;
and as they contain abundance of quartz and
felspar, may be called pitchstone-porphyry, for
which see the Siliceous Intrites.

Pitch-stone is universally regarded as a pri-
mitive rock ; but it is also often found second-
ary, and constituting the substance of petrified
wood. In the island of Arran it forms large
veins in sand-stone; and it also occurs in Mull
and Eig. This curious and important substance
seems unknown to Wallerius ; but Gmelin, in
his edition of Linnaeus, has called H opahts piceus,
and mentioned many of its sites, as Iceland, the
isle of Elba, Auvergne, Transylvania, Hungary,
the Reisgeberg mountains in Germany, and New
Spain. It sometimes occurs in basalt.


Pitch-stone, from Meissen in Saxony, where it
was first observed.

The same, dark red, from Korbetz in Saxony.

The same, spotted with black, from Upper

The same, deep red, mingled with greenish

* Kirwan Geol. Ess. 180.


transparent opal, from Upper Hungary. Born
I 213.

The same, of a clear blue, from Telkobanya in
Upper Hungary.

Green, from Meissen in Saxony.

Green pitch-stone, with adherent sand-stone,
from Arran.

The stalactitic kinds, and the petrified wood
from Hungary, cannot be said to constitute rocks.


Laminar pitch-stone, in thin horizontal layers,
alternately white and violet, from Telkobanya.

A laminar kind was also discovered by Mr,
Jameson in the island of Arran.


These rocks present crystals of felspar, some-
times quartz, or calcareous spar, in a siliceous
ground or base. The most remarkable kinds
are those called keralite or hornstein porphyry,
and pitch-stone porphyry. They are vaguely
classed under the general name porphyry by
German the German theorists, while the crystals are so
unimportant, that in geology they should be


ranked immediately after the parent rock. The
primitive porphyries, according to Werner, are
those of hornstein and felsite ; to which may be
added granitic porphyroid, already described
after granite. If a jasper porphyry be found, it
must also be admitted. The classical porphyries
are unaccountably treated with great disregard,
being considered as primitive grunsteins; and
the real red porphyry seems as unaccountably
omitted. Secondary porphyry includes those
with bases of pitch-stone and of clay. The Ger-
mans have never been celebrated for clear ideas;
and it is truly painful to observe such an utter
confusion of important substances in elaborate
systems, while the most trifling objects are elu-
cidated with infinite patience and assiduity.

Turpe est difficiles habere nugas,
Stultus et labor ineptiamm.


The keralite is generally reddish or greenish.
It is sometimes said to form mountains in Siberia
and other countries.




Saussure mentions a porphyry with a base of
earthy felspar. What is called klingstein por-
phyry, or porphyry slate, by Werner, is the most
common and at the same time the most remark-
able substance in this division. It has been al-
ready described under the Mode Felsite.


This has been chiefly observed in Auvergne,
where the base is generally a dark or bottle-green
pitch-stone, with lighter crystals of felspar. It
also occurs in the island of Arran.

In those parts of Auvergne which are truly
volcanic (a position to which the most rigid dis-
ciples of Werner, who have visited that region,
such as Buch and Daubuissoh, among others,
have been converted), pitch-stone is often found
decomposed, and partly reduced to a brownish
mass, resembling ochre of iron, and probably
arising from the five parts of iron which it con-
tains. This substance will be more minutely de-
scribed in the division of Decomposed Rocks.



This division will comprehend many import- Description,
ant substances of various structures, from the
celebrated Egyptian bricia, containing large
pebbles of jasper, granite, and porphyry, to the
siliceous sand-stone of Stonehenge. The glu- Origin,
tenites are of various formations; and the pud-
ding-stone of England would rather seem, as
already mentioned, to be an original rock, the
pebbles or rather kernels having no appearance
of having been rolled in water. Patrin* has
expressed the same idea concerning those pud- Pudding-stones
ding-stones which so much embarrassed Saus-
sure, as he found their beds in a vertical posi-
tion, while he argues that they could only have
been formed on a horizontal level. This curious
question might, as would seem, be easily decided
by examining if the kernels have been rolled, or
if, on the contrary, they retain their uniform
concentric tints, observable in the pudding-stone
of England, and well represented in the speci-
men which Patrin has engraved. But the same
idea had arisen to me before I had seen Patrin's

i. 154.


ingenious system of mineralogy. In like man-
ner rocks now universally admitted to consist of
granular quartz, or that substance crystallised
in the form of sand, were formerly supposed to
consist of sand agglutinated. Several primitive
rocks contain glands of the same substance, and
that great observer, Saussure, has called them
Glandulites, an useful denomination, When the
glands are of the same substance with the rock;
while Amygdalites are those rocks which con-
tain kernels of quite a different nature. He
observes, that in such a rock a central point of
crystallisation may attract the circumjacent
matter into a round or oval form, perfectly de-
fined and distinct; while other parts of the sub-
stance, having no point of attraction, may co-
alesce into a mass. The agency of iron may
also be suspected, that metal, as appears from
its ores, often occurring in detached round and
oval forms of many sizes, and even a small pro-
portion having a great power*.

On the other hand/ many kinds of pudding-
stone consist merely of rounded pebbles. Saus-
sure describes the Rigiberg, near the lake of
Lucerne, a mountain not less than 5800 feet in

* Buffon had on his estate a large and important mine, in which
the iron ore was solely in the form of peas.


height above the sea, and said to be eight leagues
in circumference, which consists entirely of roll-
ed pebbles, and among them some of pudding-
stone, probably original, disposed in regular
layers, and imbedded in a calcareous cement.
The pudding rocks around the great lake Baikal,
in the centre of Asia, present the same phe-
nomenon ; but it has not been observed whether
the fragments be of an original or derivative
rock. The derivative are supposed by theorists
to have proceeded from vast currents, flowing
from the primitive mountains, as on the dimi-
nution of the primitive waters these mountains
first appeared in the shape of islands, while the
remaining parts of continents required many
ages before they emerged from the ocean. It is
remarkable that this corresponds with the most
ancient ideas ; for the Argonauts are represented
as sailing from the Euxine Sea to the British
Ocean ; and Cesar describes Britain as an island
shared between land and water, the rivers being,
as in most countries newly inhabited, of enor-
mous size.

The siliceous sand- stones form another im- Sand-stones.
portant division of this mode. They may some-
times, as already mentioned, be confounded with
granular quartz, which must be regarded as a
primary crystallisation. The sand, which has

VOL. I. Q,


also been found in micaceous schistus, and at a
vast depth in many mines, may be well regarded
as belonging to this formation ; for it is well
known, that if the crystallisation be much dis-
turbed, the substance will descend in small irre-
gular particles.

Siliceous sand-stones are far more uncommon
than the calcareous or argillaceous. The limits
of the chalk country in England are singularly
marked by large masses of siliceous sand-stone,
irregularly dispersed. Those of Stonehenge af-
ford remarkable examples of the size and nature
of those fragments, but the original rock has not
been discovered. Trap or basaltin often reposes
n siliceous sand-stone.


This division of course includes siliceous bricias
and pudding-stones. The most eminent and sin-
gular of these occur in Egypt, in the celebrated
universal bricia of the Valley of Cosseir, and in
the siliceous bricia of the same chain, ^in which
are imbedded those curious pebbles known by the
name of Egyptian jasper ; and which also some*
times contains agates. This last, from its colour
and decomposition, might perhaps be more pro-
perly classed among the Siderous Intrites; but


till a proper analysis be formed, it may as well
follow the universal bricia, to which it may be
regarded as a remarkable rival. Bricias, with red
jasper, also occur in France, Switzerland, arid
other countries ; but the cement is friable, arid
they seldom take a good polish. All these rocks
present both round and angular fragments, which
shows that the division into bricias and pudding-
stones cannot be accepted : a better division, when
properly ascertained, would be into original and
derivative glutenites. In a geological point of
view, the most remarkable pudding-stones, which
might more classically be called Kollanites, from
the Greek*, are those which border the chains of
primitive mountains, as already mentioned. The
English pudding-stone (for a particular account of
which see the Anomalous Rocks) is unique ; and
beautiful specimens are highly valued in France,
and other countries. It is certainly an original
rock, arising from a peculiar crystallisation, being
composed of round and oval kernels of a red, yel-
low, brown, or grey tint, in a base consisting of
particles of the same, united by a siliceous cement.
A coarser kind also occurs, consisting of grey
pebbles in a far more abundant grey cement; it

- * KoA/.a, cement; the more proper, as it also implies iron,
often the chief agent.


seems harder than the pebbles themselves, which
are apt to drop out entire, the circumference of
crystallisation having been as exactly denned by
the laws of attraction, as in the detached peas, or
little geods of iron, already mentioned. Patrin
supposes that they were formed separately, and
afterwards cemented by siliceous matter ; but as
many other crystals are easily detached from the
gangart, there seems to be no necessity for this

Saussure, 1943, has treated the utility of the
pebbles, study of pebbles. In the glens of high mountains
they are of the same stones with these mountains;
but in the plains, and the large adjoining valleys,
they are of quite a different nature, and seem to
have been transported by some great revolution.

" It is an important observation for the theory
of the earth, that in the upper parts of valleys
surrounded with high mountains, no rolled pebbles
are found, which are foreign to the valley itself in
which they are met with ; those observed are never
other than spoils of the neighbouring mountains.
In the plains, on the contrary, and at the openings
of valleys which adjoin the plains, and even some
way up the sides of the mountains which border
on these plains, pebbles and blocks are found,
which might be said to have fallen from the hea-


vens, so different is their nature from every thing
found in the environs."*

The same able observer describes, 957, the Triumphal
triumphal arch of Augustus, at Aosta, as con-
structed of large squares of a singular kind of
pudding-stone, * or large sand-stone, being an as-
semblage of fragments, mostly angular, of all sorts
of primitive rocks, quartzy, slaty, and micaceous,
the largest about the size of a hazel nut. The
cement he does not mention. Most of the ancient
edifices of Aosta and its environs are of this stone,
and the common people are persuaded that it is a
composition, as was also the first general belief
concerning granite; but Saussure observed the
rocks in the mountains on the north, above the
road to Yvree. ^

Aspect 1. Green universal bricia, from the old
Egyptian monuments.

The celebrated sarcophage, in the British Mu-
seum, is of this stone. As it chiefly consists of
green jasper, it may perhaps more properly be-
long to the Siderous Glutenites.

The same, from the Valley of Cosseir.

Aspect 2. The same, with rolled granite and
angular fragments of porphyry, from the same.

* Sauss. 717.


This is very rare, having been rejected by the an-
cient artists. There are also other diversities.

Aspect 3. Egyptian kollanite, or pudding-
stone, containing balls of brown jasper, and some-
times agates, with angular or round crystals of
unctuous quartz, in a brown ferruginous base, also
of an unctuous appearance, owing to the abund-
ance of that quartz which seems united with iron
jn forming the cement, from the valley of Suez.

Aspect 4. The same, without the balls qf jas-
per or agate, a fragment of the celebrated statue
of Memnon, in Upper Egypt.

Aspect 5. Jasper bricia, intermixed with other
stones, from Forez, in France.
The same, from Switzerland.

Aspect 6. Quartz bricia, consisting of frag-
ments of that substance joined by the same ce-
ment, from Smoland, in Sweden.


Sand-stones. In the Mode of Glutenites it would be difficult,
as the celebrated Rome de Lisle has long ago
remarked, to fix a precise boundary between pud-
ding-stones and large-grained sand-stones.


Even the Egyptian kollanite above mentioned
might, without the balls of jasper and agate, be
considered as a large-grained sand-stone, singu-
larly formed of unctuous quartz. The large-
grained siliceous sand-stones are however far more
rare than those of a finer construction. It is not
unusual to find in them, as in other sand-stones,
nodules or veins of green earth or chlorite, a sub-
stance also common in sand; and, like its parent
iron, more widely diffused than is commonly ima-

Mr. Kirwan's account of siliceous sand-stone is
too interesting to be omitted.

" This stone is generally reckoned among the
secondary ; yet where no organic remains are found
in it, where it does not rest on any secondary
stone, where no secondary stone enters in its com-
position, I do not see why it may not be aggre-
gated to the primary. Sand, amongst the con-
vulsions occasioned by the volcanic eruptions
before the creation of animals, must have been
formed ; and even independently of these, some
must have been deposited, during or after the
crystallisation of the various substances contained
in the elastic fluid. See 5th Sauss. 294. Mount
Jorat and the Coteau de Boissy, near Geneva,
1 Sauss. 246. 349, seem to be primeval; so also
the sand-stone found in the island of Bornholm,


5 Berl. Beobacht. Also that mentioned in 2
Sauss. 763, which graduates into gneiss, must
also be primary, though it contains tumblers (cail-
lous mule's). The sand-stone near Lischau, in
the vicinity of Prague, graduates into horn-stone,
and even into granite. Mr. Rosier even thinks it
to have been originally a granite, whose felspar
was decomposed into clay, which then cemented
the quartzy grains; a most ingenious and pro-
bable conjecture. 1 Bergbau. 339 and 341.

" Most of the arenilitic mountains of Bohemia,
on both sides of the Elbe, appear to be primitive,
by Reuss's description. See Reuss, 96, &c. In
the east and north parts of Bohemia, many of
them are split, or form columns resembling ba-
salts. 2 Berg. Journ. 1792, 70.

" In Bohemia, sand- stones with an argillaceous
cement alternate with those whose cement is sili-
ceous. Reuss. In Kinneculla, the lowest stratum
incumbent on granite seems also to be primitive ;
over it the secondary strata repose. 29 Swed.
Abhand. C. 29- 5 Bergm. 126.

" In Brainsdorf, in Saxony, it passes into schis-
tose mica, and alternates with argillite. 2 Crell.
Beytr. 64. In Reigelsdorf it forms the funda-
mental rock on which semiprotolite immediately
lies, which is covered with other secondary strata.
2 Berg. Jour. 1790, 285.. Near Oyben, and in


other tracts of Saxony, no petrifactions or conchy-
laceous impressions are found in it, though in that
of Perna, adjoining, they are found. Char p. 24
and 26 : it sometimes reposes on horn-slate.
Charp. 24.

" The mountain Steinthal, in the Vosges, of red
gand-stone, is considered, by Baron Diedrech, as
primeval. 2 Diedr. Gites des Minerals, 209, 210.
The sand-stone mentioned in 6 Sauss. 81, which
alternates with primitive lime-stone, must also be
primitive."* 1

Brongniart, in his Mineralogy, has adopted
rather a singular distribution of the gr&s, that is,
grit or sand-stone, and arranges it immediately
after quartz. He informs us, in a note, that he
only here describes the pure and homogeneous
sand-stone, composed solely of quartz ; the other
stones, commonly called sand-stones, being placed
among the rocks, where they will be described
under the name of psammites. The stone which
he defines is composed of very small grains of
quartz, " agglutinated by an invisible cement."
It has therefore the hardness and infusibility of
quartz in its grains ; but its texture changes the
aspect of its fracture. This fracture, always gra-
nular, sometimes scaly and even shining, without

* Geol. Ess. 208.


ceasing to be granular, is sometimes level, some-
times conchoidal. When this grit is solid, it
strikes fire with steel ; when friable, its hardness
can only be judged by the ease with which it
scratches steel, and the hardest glass ; but it does
not scratch beryl. These characters suffice to
distinguish it from dolomite, granular sulphate of
barytes, emery, and some horn-stones, the only
substances to which it bears some resemblance.

He then enumerates several varieties : as, 1 .
the grks lustrb of Haiiy, which betrays its granular
texture by its translucency. It forms beds at
Montmorency, near Paris, and arrects near Cher-
bourg. The very ingenious Gillet discovered that,
under a violent blow of the hammer, a regular
pyramid or wide cone is often extricated. 2. The
white sand-stone found to the south of Paris, and
often used for grindstones ; while that of Fontaine-
bleau, which is in very thick horizontal beds,
serves to pave the streets of Paris. It is some-
times mixed with lime, which makes it effervesce ;
but this alteration is more rare than is commonly
conceived, and is only observed in the quarries
called Belle Croix and Nemours, where are also
found the curious crystals in which the quartzose
sand assumes the calcareous form. 3. Ribbon-
grit, so called because various colours are dis-
played in straight lines or in zigzag : it is com-


mon in Thuringia and in Magdeburg. 4. Red
grit, which is of a coarse grain, and the particles
united by iron. This is the deadlayer of the Ger-
mans, which it is ridiculous to class here, as it
totally differs from his introductory definition.
5. Flexible grit of Brazil. 6. Filtering-stone, full
of numerous and irregular pores, but seemingly
composed of quartz only. It is found in Saxony,
Bohemia, New Spain, and the Canaries : it is also
found in Spain, in Guipuscoa, where they make
statues with hollow heads, so that water being
poured it passes through the eyes, and the figures
seem to weep.

Such, he says, are the principal varieties afforded
by grit or sand-stone, considered as homogenous,
and not as a mingled rock; and he adds some
examples of sand-stones originally crystallised
with that texture : but when he includes the red
ferruginous sand-stone, he forgets that it some-
times contains fragments of porphyry and other
rocks ; and parts of the remainder of the article
refer to argillaceous and even calcareous sand-
stone. This stone therefore, which he places be-
tween quartz and flint, ought to have been classed
with the former under the usual denomination of
.granular quartz.

Mr. Jameson has observed*, that there is a

* Geog. p. 39.


sand-stone cemented by quartz; so that a chemi-
cal and mechanical formation may occur in the
same rock. He mentions, in another work*, that
there is a vein at Lauterberg, in the Hartz, nine
fathoms wide, filled with quartz in the state of
sand. Pepits of copper are intermixed, and the
miners only use picks. It is crystallised, and not
the product of decomposition ; if permeated by a
siliceous juice, it would have been sand-stone.
Fine examples of siliceous sand-stone may be
found in Salisbury Craigs, near Edinburgh.

Aspect 1. Coarse siliceous sand-stone, from
Sweden, &c.

Aspect 2. Fine, from Stonehenge, &c.

The same, from Salisbury Craigs, near Edin-

Elastic siliceous sand-stone, sometimes called
elastic quartz, from Brazil.

Siliceous sand-stone, like most other rocks, is
also found schistose and laminated.

Add the following varieties, from Saussure :

A remarkable sand-stone, composed of very
small grains of white quartz and felspar, with
little specks of greenish mica, which absorbs water

* Dumfriesshire, from Voigt.


with avidity, becoming greenish and translucent,
so as to resemble a felsite or jad. 1242.

A sand-stone of a violet colour, common be-
tween Antibes and Frejus. It contains bits of
porphyry, and fragments of other sand-stones.

Siliceous sand-stone, which resembles gneiss,
and alternates with lime-stone and slate. 763.

Beds of a beautiful sand-stone, composed of
adherent grains of quartz. 1370.

A green sand-stone, of little fragments of quartz,
in a cement of felsite. 1539.

Sand is not only the produce of crystallisation,
but may even be produced artificially by an ope-
ration of that kind. 1375.

In 1751, a mountain between Sallenche and
Servoz fell down, with such a thick and horrible
dust, diffused to the distance of five leagues, that
people thought the end of the world was arrived.
It was undermined by a lake ; and vast masses of
stone fell down day and night with a noise like
thunder. Among the ruins of this mountain Saus-
sure found the following singular sand-stone :

" Fragments of a kind of greenish sand-stone,
externally spotted, very hard, and of a very fine

* The bricia of Rosenberg, which fell in 1806, somewhat re-


6 This sand-stone effervesces with aquafortis
very weakly; but the effervescence may be in-
creased, if the acid in which it is put is heated ;
but which does not deprive it either of its co-
herence or its hardness, for it strikes fire, even
after this proof. The grains of fine sand and mi-
ca, of which this sand-stone is composed, must
then be united by a quartzy or argillaceous glu-
ten, and the calcareous particles which produce

Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 16 of 35)