John Pinkerton.

Petralogy. A treatise on rocks (Volume 1) online

. (page 18 of 35)
Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 18 of 35)
Font size
QR-code for this ebook

important particulars; but enough remains to
show the construction of this magnificent and
singular chain, which astonished our author by
such abrupt irregularities, and such various al-
ternations of their component parts, as he had
never beheld in the mountains of Hungary,
Saxony, or the Pyrenees. In no country, he
adds, does a revolution of nature appear to have
been so general as in South America, and the
traces are every where discoverable.

After further premising that he travels from
Buenos Ay res to Lima, across the chief region
of the Andes, his scattered information on this
important topic shall be brought before the
reader in one point of view.

" During the journey to Tucuman we found


the mountains composed of primitive granite*
but as we proceeded, the granite became inter-
mixed with argillaceous slate of various colours ;
that however which chiefly predominates in the
Cordilleras is of a bluish cast, as far at least as
we had an opportunity of examining them.
Strata of lime-stone, and large masses of ferru-
ginous sand-stone, are in many places super-
incumbent on the argillaceous slate. We like-
wise found on the road coal, gypsum, and rock
salt; the last even on the summits of the most
elevated ridges."

In the bed of the river Rosario he likewise
observed blue clay slate ; and he was surprised
to find the highest snow-capt mountains, within
nine miles of Potosi, covered with a pretty thick
stratum of granitic stones, rounded by the action
of water; while there is a continual descent to
Tucuman, where the granitic ridge ends: and
from Tucuman to Potosi it consists of simple
clay slate.

" The mountain Potosi, at whose foot the
city is built, resembles a sugar-loaf: it is almost
eighteen miles in circumference, and chiefly
composed of a yellow very firm argillaceous
slate, full of veins of ferruginous quartz, in
which silver ore, and sometimes brittle vitreous
ore, are found interspersed."

On his journey from Potosi to Lima, he found


at Alcacado clay slate, interspersed with masses
of granite ; and afterwards red sand-stone on the
clay slate. They afterwards alternate, and the
slate is covered with thin moss.

The rich city of La Paz is built at the bottom
of the highest part of the Andes, covered with
everlasting snow. In a fragment of the rock,
being a glutenite of yellow clay and rounded
flints, lumps of pure gold were found, weighing
from two to twenty pounds. Puno, which is
also one of the highest parts of the Andes, pre-
sents mountains of fine clay slate, abounding in
rich ores of gold and silver.

Passing through Cuzco he arrives at Carretas.
" The base of argillaceous slate is covered with
an alluvial superstratum, which consists of marl,
gypsum, lime-stone, sand, a large quantity of
rock salt, and of fragments of porphyry, &c.
in which pure silver and rich silver ores occur
in abundance. There are few instances in
Europe of such mountains so generally abound-
ing with the precious metals, or their ores, as in
this quarter of the globe. The whole ridge ap-
pears to be full of alluvial veins of heavy silver
ores, in which pieces of pure silver, solid cop-
per, and lead ore, occur, intermixed with a
great quantity of white silver ore, and capillary
virgin silver. Thirty-six miles before we reach


Guancavelica, behind Parcos, lie mountains of
weather-beaten argillaceous slate, mixed with
sand. The sections of these mountains consist
entirely of separate, more or less sharp-pointed,
pyramids of a flesh-coloured sand-stone.

" The ridge of mountains covered with snow,
over which the road to the Pacific Ocean passes,
consists of simple sand-stone, through which
metallic veins, in some places with quartz or
felspar, in others with steatite and schorl, &c.
openly appear. On the contrary, the chain of
mountains to the north of Guamanga and Guan-
cavelica is said to consist, to the extent of one
hundred miles, of simple lime-stone, and equally
abounds with metallic ores, especially in the
province of Tarrna."

" Behind Guancavelica the mountains gra-
dually become composed of less various mate-
rials, and at last consist only of simple sand-
stone, with layers of marl, lime-stone, and spar,
or of simple lime-stone ; they continue however
equally rich in gold, silver, quicksilver, rock-
salt, &c."

It further appears from the original work that
the clay slate, which chiefly composes this mag*
nificent chain of mountains, is of various beauti-
ful colours ; blue, dark red, flesh colour, grey,
and yellow.


In chemical analysis it has sometimes hap-
pened that the chemist has ably performed his
task, but has mistaken the name of the sub-
stance. In like manner it was here necessary
to identify the rock, before proceeding to its
description. It has before been observed that it
may be divided into two kinds, which at the
same time vary considerably in their structure,
namely, primitive and secondary.


Texture, schistose, sometimes in thin layers, Character*.
but more generally they are thick and coarse;
fine-grained, sometimes almost impalpable.

Hardness, marmoric, sometimes gypsic. Frac-
ture, slaty, sometimes approaching to earthy.
Fragments, amorphous, tabular, with sharp angles.

Weight, carbonose to granitose.

Lustre, sometimes dull, often silky. Opake.

The colour is most usually grey, of various
tints ; but it may also be found of a straw yellow,
and various hues of red. It sometimes presents
streaks of a bluish white, or is mottled with va-
rious illinitions.

Yellow clay slate, from Potosi.
Grey, from the Andes, Saxony, Scotland, and
Dther metallic countries.


Pale blue, with cubic pyrites, from Yorkshire.

The same, with dendritic pyrites.

The same, singularly convolved, from the Alps
of Dauphiny, and many other regions.

Thick clay slate, intersected in all directions
with veins of quartz, from Scotland.

The same, with calcareous spar, from Durham.

The same, with veins of quartz containing eme-
ralds, from the celebrated emerald- mines at Muzo,
in the Viceroy alty of New Grenada. It does not
appear that Peru ever produced any emeralds.

Massive clay slate, or perhaps rather clay rock,
from Ronneburg.

Clay slate, in rhomboidal fragments, from Dit-

Thick clay slate, with a coarse-grained earthy
fracture, from Upper Lusatia.

Green clay slate, with calcareous spar, from

The same, with cinnabar, from Idra.

Clay slate, with yellow blend, from Transyl-

From the Specimens of clay slate, collected on the river


Ganges, and its vicinity, by Colonel Hardwick,
on his journey to Siranagur.

Clay slate, from the rocks about Ghinouly.

The same, of a silky appearance, and seemingly


much mingled with magnesia, from the rocks near
Siranagur. It is of an ash grey colour, and finely

Greenish micaceous clay slate, from Coadwara.
Purple clay slate, veined with dull green, from
the rock of Bedeyl.

Lilac-coloured clay slate, which alternates with
laminated smectite, in the hills near Adwaanee.
The strata are inclined 45.

Brown clay slate, found in thick strata near
Kurd war.

Clay slate, in thin layers of different colours,
from Bedeyl.

Purple clay slate, from high mountains near

Micaceous clay slate, of a bluish grey, from

Clay slate bricia, intersected with quartz veins,
in^a cement of clay slate tufa, from Bedeyl.

Clay slate, intersected with quartz in all direc-
tions, from the same.

Clay slate, of a brownish red, and various other
colours, from Ansore.

Brown clay slate, in bowlders, found in the bed
of the Alecnundra, near Siranagur*.

* These specimens were presented by Colonel Hardwick to the


European. To the European may be added,

Micaceous clay slate, from Mont Blanc.

Clay slate, mingled with chlorite, from Mont


Purple clay slate, with spots of quartz and

mica, and thin layers of talcous schistus, from the


iSoft grey clay slate, from the same.
Grey clay slate, sometimes spotted with decom-
posed pyrites, from the summit of Snowdon,
where it rests in beds nearly horizontal, on arrects
or uprights of schistose keralite.

A remarkable clay slate, of a yellowish brown,
with long streaks, so as to have the appearance of
oak board, with some knots of a deeper brown,
and others white. It is mingled with a little
quartz and mica. Sauss. 1482.


This either occurs uniform, or with impressions
of vegetables, or sometimes of shells.

Aspect 1. Uniform. Thick slaty shale, from

Shale, from numerous coal-mines.
Variety. Bituminous shale, from the same.


Aspect 2. With impressions. Shale, with the
impression of the skeleton of a fish in a lighter
colour, from Hessia.

Shale, with the impression of an ammonite,
from Chamoimi.

The same, with impressions of various vege-
tables, chiefly gigantic ferns, from various coal-

Variety. Bituminous shale, with various im-

There are two substances often found in clay
slate, and considered as of a kindred nature, but
they never appear in the form of rocks. 1 . Black Black chalk,
chalk, so called because it is used in drawing,
and which, according to Weigleb, contains 1 1 of
carbon. 2. "Hone, which is as proper and so- Hone,
norous a name as novaculite, or whet-slate. Some
clay slates and sand-stones form the coarser whet-
stones, used by cutlers. The finest hones are
said to be brought from Turkey, but they are also
said to be found in the neighbourhood of Namur,
in Flanders. Brochant says that it is also found
in Bohemia, in Saxony (Seifensdorf, near Frey-
berg), in Siberia, in Stiria : lastly, at Lauenstein,
in the Margraviate of Bareith, where it is wrought.
It often seems to form the passage to indurated
talc, and is sometimes covered with efflorescences


of sulphate of magnesia, which has led to a be-
lief that talc is one of its constituent parts; as
Werner also suspects, from its unctuous feel, and
being often of a greenish tint. It not unusually
presents two layers ; the upper of a pale greenish
yellow, and the under of a blackish brown. The
fracture is often scaly, which is seldom observed
in other schistose substances ; but that of Bareuth
sometimes presents a slaty fracture, partly ap-
proaching to the conch oidal, and partly to the
earthy. Hone seems nearly related to a highly
indurated fullers' earth, and is said by some to
decompose into tripoli*.

* Saussure says, 15p4, that the common touch-stone is com-
posed of little white grains of quartz and felspar, enveloped in
ferruginous clay. The hard black nodules, which are found in
slate, likewise afford very good totfch-stones. The little hard grains
form a kind of file, which seizes on the substance of the metal,
while the black gluten displays the colour. And as acids do not
affect the stone, the trace may easily be tried by the nitrous acid, or
by the aqua regia.



Texture, of a fine earthy grain. Characters.

Hardness, marmoric, sometimes gypsic. Frac-
ture, generally even, sometimes flatly conchoidal.
If slaty, it approaches to clay slate. Fragments,
amorphous, rather blunt.

Weight, granitose.

Lustre, dull. Opake.

This is the thonstein of Werner, which forms
large rocks, and is the base of his clay por-
phyry, which will be described among the Ar-
gillaceous Intrites.

In some countries, such as the Salses of Mo-
dena, in the Crimea, and near Girgenti in Sicily,
hills and masses of indurated clay are produced
by a singular cause, the eruption of what are
called muddy volcanoes. Dolomieu has mi-
nutely described that of Macaluba, near Gir- Macaiuba.
genti. A circular mountain, about 150 feet in
height, is terminated by a plain somewhat con-
vex, and about half a mile in circumference,
which is surmounted by a great number of trun-
cated cones, with little craters like funnels.
The soil on which they rest is a grey dry floor,
which covers a wide and immense gulf of mud.


There arises every instant, from the bottom of
the funnels, a wet greyish clay, with a convex
surface. This bladder, bursting with some noise,
throws beyond the crater the clay, which runs
like lava down the sides of the little hills; the
intermission between the petty explosions being
between two and three minutes. This hill has
also more important fermentations, in which it
affects to imitate a volcano ; little earthquakes
are perceivable at the distance of two or three
miles, and there are serious eruptions, which
sometimes elevate a sheaf of liquid clay to the
height of 200 feet ; the explosions being repeated
three or four times in the twenty-four hours,
and accompanied with a fetid sulphurous odour.
This singular volcanello has been described by
Strabo and Solinus; and the others present the
same phenomena. Patrin says that the clay is
of a greyish blue, and that Spallanzani has found
in it the same elements as in basaltin. Dolo-
mieu has also observed that the clay hills, which
cover the surrounding country, are the produce
of those eternal ejections mentioned by Solinus*.
When clay rock is strongly impregnated with
iron it passes into jasper. The more common
colours are grey and red, and it is sometimes

* Dolomieu, Lipari, 153. Patrin Min. v. 24p.


spotted or striped. Mr. Jameson, in his Mi-
neralogy, has promised a more particular ac-
count of thonstein - 3 which he has not however
accomplished in his Geognosy, where he only
informs us that the Pentland hills, near Edin-
burgh, present examples. Dr. Babington, in
his catalogue, mentions clay porphyry from the
vicinity of Edinburgh ; but gives no examples
of the clay rock, which seems however to form
a great part of that vast chain of mountains the
Andes. In Chili entire mountains are com-
posed of brown or black clay rock.

This substance frequently occurs in coal and
other mines, where it receives a vast variety of
provincial names, according to the fancy of the
miners. In coal-mines it is commonly a shale,
and alternates with beds of sand-stone, which
also in such circumstances receives fanciful de-

Clay rock, from Saxony.

The same, from the Andes.

The same, frpm Pentland hills.

* What is called the clay-bed of the Leadhills, in Scotland,
varies from the softness of tough clay, to the hardness of striking
fire with steel ; in the language of miners, from mcll and wedge to
Hasting : and this too at a depth from forty to fifty fathoms.

Near Lesmahago, Lanarkshire, is a lead-mine in clay slate : the
metal being in a vein, of sulphate of barytes, five feet wide. G. L.


Saussure, 1944, describes a kind of clay rock
found among the pebbles of the two rivers called
Emme, in Swisserland. This substance having
hitherto little engaged the attention of mineral-
ogists or geologists, ail the accounts are very

P^iain Porcelain clay sometimes constitutes rocks ;
but it is merely a decomposed felspar, which
may be found in the Domain entitled Decom-
posed Rocks. Potters' clay seems only to occur
in separate strata ; when of a greyish white, it
is called pipe-clay. The clay of which the
famous Egyptian vases have been formed for
many thousand years, is, according to Roziere,
of a marly nature, and is found near Coptos in
the Thebaid. It approaches to the fawn co-
lour, and is of a porous and light consistence.
Porous vases which, by evaporation, impart
great coolness to water, are also made in Spanish
America, where the ladies are even fond of eat-
ing the fragments*. Molina, in his interesting
account of Chili, has described several valuable
clays, of which there is one which long retains a
sweet smell.
Boies. The I^emnian, Armenian, and other boles,

* Da Costa, p. 20, says it is a bole useful in acidities, and as a


formerly celebrated as absorbents, and which
are now supplanted by magnesia, are merely
fine clays, which contain a small portion of
magnesian earth. Hence they somewhat ap-
proach in their nature to the fullers' earth of
Berkshire, and Ryegate in Surry*.

The earth called almagra, which is used to
impart a red colour, and an unctuous feel, to
Spanish snuff, is found at Almazaran, near Car-
tliagena, in .Spain, and seems a fine ferruginous
clay, perhaps with a mixture of magnesia.


Texture, sometimes compact, sometimes vesi- Characters*
cular. When the vesicles are filled with para-
sitic stones, it is called amygdalite; but as the
base of the latter is more frequently a trap or
basaltin, it has been classed after that substance.

Hardness, marmoric, sometimes gypsic. Frac-
ture, commonly even, sometimes approaching
the flat conchoidal. Fragments, amorphous,
rather blunt.

Weight, granitose.

* Bergman has put Hampshire, in which he is followed by all
the foreign mineralogists ; but there is no fullers' earth in Hamp-




Lustre, dull, sometimes faintly glimmering.

The usual colour is grey, sometimes approach-
ing to black. It may also be brownish, from
iron ochre. Wacken sometimes contains mica,
but this mixture cannot be regarded as charac-
teristic, as appears from the amygdalites.

Wacken is ranked by the German mineral-
ogists as intermediate between basalt and clay.
Like basalt it sometimes presents siderite, but
never contains augite or olivine. It is regarded
as secondary, because petrified wood has been
found in it : but such arguments are sometimes
fallacious, for the detritus of a primitive rock
may again consolidate, as in the case of granite,
and it is easily conceivable that it may thus en-
velope substances foreign to its original form-

Wacken is often a cornecnne y or roche de corne,
of the French mineralogists. The grauwack of
the Germans is a very different substance, which
\vill be described among the Argillaceous Glu-

Wacken, from Saxony, &c.



This substance is commonly called fullers'
earth ; but as the latter word would here seem
rather a solecism, it may be preferable to adopt
the Greek denomination.

Texture, earthy, sometimes with a very fine Characters,

Hardness, cretjc. Fracture, uneven, some-
times large conchoidal. Fragments, amorphous
and blunt.

Weight, carbon ose.

Lustre, dull. Opake.

The colour has often a greenish tinge, which
may arise from a very small portion of mag-
nesia; but as this scarcely amounts to 1 in 100,
there is no reason for classing it among the
Magnesian Rocks; especially as in that from the
island of Cimolus, which is superior even to the cimoiite.
English, Klaproth could discover no magnesia,
the unctuous feel arising from the mere purity
of the clay*. In general fullers' earth would Fullers' earth,
rather be judged of a light brown colour. The

* Da Costa has observed that great fineness of the grain will
often impart an unctuous feel.

fn O


coarser sort at Ryegate, which contains crystals
of barytes, is of a reddish brown, and is not used
in commerce.

The analysis by Bergman bears that the
fullers' earth comes from Hampshire, a mistake
followed by a hundred mineralogic writers; and
it was probably from Reading, in Berkshire, for
in the vicinity of that town there are remarkable
quarries, which lie under beds of sea sand,
mingled with numerous shells of oysters. It is
also found near Woburn, in Bedfordshire, and
Ryegate, in Surry.

Da Costa informs us, that fullers' earth is dug
at Wavendon, near Woburn, in Bedfordshire.
For about six yards there are layers of reddish
sand, then a thin stratum of sand-stone, then
sand again for seven or eight yards; after which
fullers' earth appears for about eight feet, fol-
lowed by sand-stone and sand. At Ryegate
and Nutfield, in Surry, the strata are similar;
but at Detling, near Maidstone, in Kent, it un-
derlies a sandy loam, mixed with a great variety
of shells. It is prevented from being exported
by a special act of parliament*.

Near Reading oyster-shells are found at the
bottom of a high hill, a hundred feet below the

* Nat. Hist, of Fossils, 1757, 4to. p. 69.


surface. They lie on chalk, covered with sea
sand, which still retains its brackish flavour.
Above that is fullers* earth, nearly eleven feet in
depth, and then chalk, and different kinds of
clay ; then a common sort of sand : and so on
to the surface, which is gravel.

It does not effervesce with acids, nor is it dif-
fusible in water, in which it does not froth like
soap, as some have asserted. It is used in what
is called the fulling of broad cloth, an operation
which consists in extracting the grease.

Abroad, it has been found in Saxony, Alsace,
and Sweden, always forming beds of more or
less thickness. In England it commonly ap-
pears between beds of sand-stone.

The earth brought from Cimolus, which is
described by Pliny as used in medicine and in
bleaching, has again been discovered, by Mr.
Hawkins. It is mingled with small particles of
quartz ; but this circumstance does not prove it
to be a decomposed granite, as an accidental
mixture of silex occurs in many substances.

Fullers' earth, from Reading, in Berkshire. .

The same, with incumbent sea sand and

The same, from Ryegate, in Surry.

The same, of a coarser kind and darker co-
lour, with imbedded crystals of yellow barytes.


Mr. Sowerby has a large regular crystal of this
kind, equal in beauty to a topaz.

Smectite, from Cimolus, one of the islands of
the Grecian archipelago.


This substance is only known by the little
images brought from China, whence the name
is imposed. From its unctuous appearance it
was long imagined to belong to the Magnesian
Domain, till Klaproth's analysis assigned it to
the Argillaceous. It contains, silex, 62; argil,
24; lime, 1; water, 10; a combination which
nearly corresponds with the smectite of Cimo-
lus. The abundance of water seems, in this and
some other substances, to impart an unctuous
appearance; but the refinements in modern
chemistry may perhaps discover something par-
ticular in the composition of this water*.

The Germans denominated this substance

Biidstein. bildstein, that is, image-stone, which Klaproth

has translated agalmatolite, while he might have

used the far shorter term here adopted. It must

* The analysis approaches that of chalcedony, which has also an
unctuous appearance, perhaps from the admixture of argil.


iilso be premised, that sometimes the red or
flesh-coloured stone, more rarely used for the
same purposes by the Chinese, really belongs to
the magnesian kind.

Klaproth mentions two kinds of iconite, the
transparent and the opake; the former unex-
pectedly presenting a third more argil, and only
half the water of the latter.


Klaproth describes this sort as being of an olive
or asparagus green, verging through various tints
to a greenish blue. The interior aspect is very
glittering, and of a greasy lustre; the fracture


This, according to Klaproth, is reddish white,
flesh red, and with variously-coloured veins ; the
fracture is less distinctly scaly ; the lustre dull,
opake, but somewhat translucent on the edges.

Werner has rightly added to the colours of the
bildstein the greenish grey, of different degrees
of intensity, the yellowish passing into yellowish
grey mingled with green, and into pale yellowish
brown. The greyish white seems to be one of
the most common tints of this substance.


Du Halde, in his description of China, men-
tions that the district of Tay-tong-fu, belonging
Yu-she. to Shan-si, furnishes the most beautiful Yu-she,
which that author, in the confused mineralogy of
the time, calls a kind of white jasper. He adds,
that it resembles agate, is transparent, and some-
times appears spotted.

Goez, who travelled to Tibet in 1602, in de-
scribing Yarkand, the capital of the kingdom of
Kasgar, in Little Bucharia, mentions, that a com-
modity, particularly acceptable in China, was a

Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 18 of 35)