Encyclopaedia Britannica, 11th Edition, "Capefigue" to "Carneades"

Chapter XI: Part 11

Text size

In addition to the above broad subdivisions, Murchison and Sedgwick,
when working upon the rocks of Devonshire and Cornwall, recognized,
with the assistance of W. Lonsdale, another phase of sedimentation.
This comprised dark shales, with grits and thin limestones and thin,
impure coals, locally called "culm" (q.v.). These geologists
appropriated the term "culm" for the whole of this facies in the west
of England, and subsequently traced the same type on the European
continent, where it is widely developed in the western centre.

Besides the considerable exposed area of Carboniferous rocks in Great
Britain, there is as much or more that is covered by younger
formations; this is true particularly of the eastern side of England
and the south-eastern counties, where the coal-measures have already
been found at Dover.

From England, Carboniferous rocks can be followed across northern and
central France, into Germany, Bohemia, the Alps, Italy and Spain. In
Russia this system occupies some 30,000 sq. m., and it extends
northward at least as far as Spitsbergen. Carboniferous rocks are
present in North and South Africa, and in India and Australasia; in
China they cover thousands of square miles, and in the United States
and British North America they occupy no less than 200,000 sq. m.;
they are known also in South America.

The subjoined table expresses the typical subdivisions which can be
recognized, with modifications, in the United Kingdom.

/ Upper: Red and grey sandstones, marls and clays with
| occasional breccias, thin coals and limestones with
| _Spirorbis_, workable coals in the South Wales,
| Bristol, Somerset and Forest of Dean coalfields.
Coal |
Measures. < Middle: Sandstones, marls, shales and the most
| important of the British coals.
|
| Lower: Flaggy hard sandstones (ganister), shales and
\ thin coal seams.

/ Grits (coarse and fine), shales, thin coal seams and
Millstone < occasional thin limestones. The fossil plants connect
Grit. | this group with the coal-measures; the marine fossils
\ have, to some extent, a Carboniferous limestone aspect.

/_Upper black shales_ with thin limestones (Pendleside
| group) connecting this series with the Millstone grit
| above.
|
| _The thick, main or scaur limestone_ (mountain
| limestone) of the centre and south of England, Wales
| and Ireland, which splits up in the Yorkshire dales
Carboniferous | (Yoredale group) into a succession of stout limestone
Limestone < beds between beds of sandstone and shale, and becomes
Series. | increasingly detrital in character as it is traced
| northwards.
|
| _Lower limestone shales_ of the south and centre of
| England with marine fossils, and the Calciferous
| Sandstone group of Scotland with marine, estuarine and
\terrestrial fossils.

(See BERNICIAN, TUEDIAN and AVONIAN.)

At an early period, owing to the immense commercial importance of the
coal seams, it became the practice to distinguish a "productive"
(_flotzfuhrend, terrain houiller_) and an "unproductive," barren
(_flotzleerer_) Lower Carboniferous; these two groups correspond in
North America to the "Carboniferous" and "Sub-Carboniferous"
respectively, or, as they are now sometimes styled, the
"Pennsylvanian" and "Mississippian." But it was soon discovered that
the "productive" beds were not regularly restricted to the upper or
younger division, and, as E. Kayser points out, the real state of the
matter is more accurately represented by the subjoined tabular scheme.

While the continental type of deposit, with its coal beds, was the
earliest to be formed in certain areas, and the marine series came on
later, in other regions this order was reversed. It should be
observed, however, that the repeated intercalation of marine deposits
within the continental series and the frequent occurrence of thin
coaly layers in the marine series makes any hard and fast distinction
of this kind impossible.

The so-called "unproductive" or barren strata, that is, those without
workable coals, are not always limestones; quite as often they are
shales, red sandstones and red marls.

In subdividing the strata of the Carboniferous system and correlating
the major divisions in different areas, just as in other great
systems, use has to be made of the fossil contents of the rocks;
stratigraphical units, based on lithology, are useless for this
purpose. The groups of organisms utilized for zoning and correlation
by different workers include brachiopods, pelecypods, cephalopods,
corals, fishes and plants; and the results of the comparison of the
faunas and floras of different areas where Carboniferous rocks occur
are generalized in the table below.

The relative value of any group of animals or plants for the
correlation of distant areas must vary greatly with the varying
conditions of sedimentation and with the precise definition of the
zonal species and with many other factors. It is found that the
subdivisions in this system demanded by palaeobotanists do not always
coincide with those acknowledged by palaeozoologists; nevertheless
there is general agreement as to the main divisional lines.

_Breaks in the Stratigraphic Sequence._--The sequence of Carboniferous
strata is not everywhere one of unbroken continuity. From central
France eastward towards the Carpathians only later portions of the
system are found. These generally rest upon crystalline rocks, but in
places they contain evidence of the denuded surfaces of Lower
Carboniferous, as in the basin of Charleroi, where the equivalent of
the Millstone Grit contains fragments of chert which can only have
come from the waste of the earlier limestones. This unconformity is
generally found about the same horizon in the continental Culm areas,
and it occurs again in the western part of the English Culm.

_Tabular Statement of the Principal Subdivisions of the Carboniferous
System._

In the eastern border of the Rhenish Schiefergebirge the Permian rests
unconformably upon Lower Carboniferous rocks. In the United States, in
Missouri, Pennsylvania, West Virginia, Kentucky, Ohio and elsewhere,
there is an unconformable junction between the Lower and Upper
Carboniferous, representing an interval of time during which the lower
member was strongly eroded; it has even been proposed to regard the
Mississippian (Lower Carboniferous) as a distinct geological period,
mainly on account of this break in the succession.

_Thickness of Carboniferous Rocks._--The great variety of conditions
under which the sediments and limestones were formed naturally
produced corresponding inequalities in the thickness. In the Eurasian
land area the greatest thickness of Carboniferous rocks is in the
west; in North America it is in the east. In Britain the Carboniferous
limestone series is 2000-3500 ft. thick; in the Ural mountains it is
over 4500 ft.; the Culm in Moravia is credited with the enormous
thickness of over 42,000 ft. The Upper Carboniferous in Lancashire is
from 12,000 to 13,000 ft.; elsewhere in Britain it is thinner. In
western Germany this portion attains a thickness of 10,000 ft. In
Pennsylvania the sandstone and shale, at its maximum, reaches 4400
ft., but even within the limits of the state this formation has
thinned out to no more than 300 ft. in places. In Colorado the Lower
Carboniferous is only 400-500 ft. thick; while the limestones of the
Mississippi basin amount to 1500 ft. and in Virginia are 2000 ft.
thick.

_Life of the Carboniferous Period._--We have seen that in the
Carboniferous rocks there are two phases of sedimentation, the one
marine, the other continental; corresponding with these there are two
distinct faunal facies.

(1) _Fauna of the Marine Strata._--Numerically, the most important
inhabitants of the clear Carboniferous seas were the crinoids, corals,
Foraminifera and brachiopods. Each of these groups contributed at one
place or another towards the upbuilding of great masses of limestone.
For the first time in the earth's history we find Foraminifera taking
a prominent part in the marine faunas; the genus _Fusulina_ was
abundant in what is now Russia, China, Japan, North America;
_Valvulina_ had a wide range, as also had _Endothyra_ and
_Archaediscus; Saccammina_ is a form well known in Britain and
Belgium, and many others have been described; some Carboniferous
genera are still extant. Radiolaria are found in cherts in the Culm of
Devonshire and Cornwall, in Russia, Germany and elsewhere. Sponges are
represented by spicules and anchor ropes. Corals, both reef-builders
and others, flourished in the clearer waters; rugose forms are
represented by Amplexoid, Zaphrentid and Cyathophyllid types, and by
_Lithostrotion_ and _Phillipsastraea_; common tabulate forms are
_Chaetetes, Chladochonus, Michelinia_, &c. Amongst the echinoderms
crinoids were the most numerous individually, dense submarine thickets
of the long-stemmed kinds appear to have flourished in many places
where their remains consolidated into thick beds of rock; prominent
genera are _Cyathocrinus, Woodocrinus, Actinocrinus_; sea-urchins,
_Archaeocidaris, Palaeechinus_, &c., were present; while the curious
extinct Blastoids, which included the groups of _Pentremitidae_ and
_Codasteridae_, attained their maximum development.

Annelids (_Spirorbis, Serpulites_, &c.) are common fossils on certain
horizons. The Bryozoa were also abundant in some regions (_Polypora,
Fenestella_), including the remarkable form known as _Archimedes_.

Brachiopods occupied an important place; most typical were the
Productids, some of which reached a great size and had very thick
shells. Other common genera are _Spirifer, Chonetes, Athyris_,
Rhynchonellids and Terebratulids, _Discina_ and _Crania_. Some species
had an almost world-wide range with only minor variations; such are
_Productus semireticulatus, P. cora, P. pustulosus; Orthotetes
(Streptorhynchus) crenistria, Dielasma hastata_, and many others.

Pelecypods among the true mollusca were increasing in numbers and
importance (_Aviculopecten, Posidonomya_); _Nucula, Carbonicola,
Edmondia, Conocardium, Modiola_. Gasteropods also were numerous
(_Murchisonia, Euomphalus, Naticopsis_). The Pteropods were well
represented by _Conularia_ and _Bellerophon_. Amongst the Cephalopods,
the most striking feature is the rise and development of the
Goniatites (_Glyphioceras, Gastrioceras_, &c.); straight-shelled forms
still lived on in some variety (_Orthoceras, Actinoceras_), along with
numerous nautiloids.

Trilobites during this period sank to a very subordinate position, but
Ostracods (_Cythere, Kirkbya, Beyrichia_) were abundant.

Many fish inhabited the Carboniferous seas and most of these were
Elasmobranchs, sharks with crushing pavement teeth (_Psammodus_),
adapted for grinding the shells of brachiopods, crustaceans, &c. Other
sharks had piercing teeth (_Cladoselache_ and _Cladodus_); some, the
petalodonts, had peculiar cycloid cutting teeth. The Arthrodirans, so
prominent during the Devonian period, disappeared before the close of
the Carboniferous. Most of the sharks lived in the sea continuously,
but the ganoids frequenting the coastal waters appear to have migrated
inland. About 700 species of Carboniferous fish have been described
largely from teeth, spines and dermal ossicles.

(2) _Flora and Fauna of the Lagoonal or Continental Facies._--The
strata deposited during this period are the earliest in which the
remains of plants take a prominent place. The fossil plants which are
found in the upper beds of the preceding Devonian system are so
closely related to those in the Lower Carboniferous, that from a
palaeobotanical standpoint the two form one indivisible period.

In the Lower Carboniferous the flora was composed of six great groups
of plants, viz. the Equisetales (Horse-tails), the Lycopodiales (Club
mosses), the Filicales (Ferns) and Cycadofilices, the Sphenophyllales
and Cordaitales. These six groups were the dominant types throughout
the period, but during Upper Carboniferous time three other groups
arose, the Coniferales, the Cycadophyta, and the Ginkgoales (of which
_Ginkgo biloba_ is the only modern representative). Algae and fungi
also were present, but there were no flowering plants. The true ferns,
including tree ferns with a height of upwards of 60 ft., were
associated with many plants possessing a fern-like habit
(Cycadofilices) and others whose affinities have not yet been
definitely determined. The fronds of some of these Carboniferous ferns
are almost identical with those of living species. Probably many of
the ferns were epiphytic. _Pecopteris, Cyclopteris, Neuropteris,
Alethopteris, Sphenopteris_ are common genera; _Megaphyton_ and
_Caulopteris_ were tree ferns. Our modern diminutive "horse-tails"
with scaly leaves were represented in the Carboniferous period by
gigantic calamites, often with a diameter of 1 to 2 ft. and a height
of 50 to 90 ft. The Carboniferous forerunners of the tiny club-moss
were then great trees with dichotomously branching stems and crowded
linear leaves, such as _Lepidodendron_ (with its fruit cone called
_Lepidostrobus), Halonia, Lepidophloios_ and _Sigillaria_, the largest
plants of the period, with trunks sometimes 5 ft. in diameter and 100
ft. high. The roots of several of these forms are known as _Stigmaria.
Sphenophyllum_ was a slender climbing plant with whorls of leaves,
which was probably related both to the calamites and the lycopods.
_Cordaites_, a tall plant (20-30 ft.) with yucca-like leaves, was
related to the cycads and conifers; the catkin-like inflorescence,
which bore yew-like berries, is called _Cardiocarpus_. Many large
trees which have been looked upon as conifers on account of their wood
structure may perhaps belong more properly to the Cordaitales. True
coniferous trees (_Walchia_) do appear at the top of the coal
measures.

The animals preserved in the continental type of Carboniferous deposit
naturally differ markedly from the fossil remains of the purely marine
portions of the system. The inhabitants of the waters of this
geographical phase include mollusca, which are supposed to have lived
in brackish or fresh water, such as _Anthracomya, Naiadites,
Carbonicola_, and many forms of Crustacea, e.g. (_Bairdia Carbonia_),
phyllopods (_Estheria_), phyllocarids (_Acanthocaris, Dithyrocaris_),
schizopods (_Anthrapalaemon_), Eurypterids (_Eurypterus,
Glyptoscorpius_). Fishes were abundant, many of the smaller ganoids
are beautifully preserved in an entire condition, other larger forms
are represented by fin spines, teeth and bones; _Ctenodus, Uronemus,
Acanthodes, Cheirodus, Gyracanthus_ are characteristic genera.

Frequently a temporary return of marine conditions permitted the
entombment of such salt water genera as _Lingula, Orbiculoidea,
Productus_ in the thin beds known as "marine bands."

Remains of air-breathing insects, myriapods and arachnids show that
these forms of life were both well developed and individually
numerous. Among the insects we find the Orthoptera, Neuroptera,
Hemiptera and Coleoptera represented; cockroaches were particularly
abundant; crickets, beetles, locusts, walking-stick insects, mayflies
and bugs are found, but there were neither flies, moths, butterflies
nor bees, which is no more than we should expect from the conditions
of plant life. Many insects, &c., have been obtained from the
coalfields of Saarbruck and Commentry, and from the hollow trunks of
fossil trees in Nova Scotia. Certain British coalfields have yielded
good specimens: _Archaeoptilus_, from the Derbyshire coalfield, had a
spread of wing extending to more than 14 in.; some specimens
(_Brodia_) still exhibit traces of brilliant wing colours. In the Nova
Scotian tree trunks land snails (_Archaeozonites, Dendropupa_) have
been found.

In the later Carboniferous rocks the earliest amphibians make their
appearance in considerable numbers; they were all Stegocephalians
(Labyrinthodonts) with long bodies, a head covered with bony plates
and weak or undeveloped limbs. The largest were about 7 or 8 ft. long,
the smallest only a few inches. Some were probably fluviatile in habit
(_Loxomma, Anthracosaurus, Ophiderpeton_); others may have been
terrestrial (_Dendrerpeton, Hylerpeton_). Certain footprints in the
coal measures of Kansas have been supposed to belong to lacertilian or
dinosaurian forms.

_The Physical Conditions during the Period._--In western Europe the
advent of the Carboniferous period was accompanied by the production
of a series of synclines which permitted the formation of organic
limestones, free from the sediments which generally characterized the
concluding phases of the preceding Devonian deposition. The old land
area still existed to the north, but doubtless much reduced in height;
against this land, detrital deposits still continued to be formed, as
in Scotland; while over central Ireland and central and northern
England the clearer waters of the sea furnished a suitable home for
countless corals, brachiopods and foraminifera and great beds of sea
lilies; sponges flourished in many parts of the sea, and their remains
contributed largely to the formation of the beds of chert. This
clearer water extended from Ireland across north-central England and
through South Wales and Somerset into Belgium and Westphalia; but a
narrow ridge of elevated older rocks ran across the centre of England
towards Belgium at this time.

Traced eastward into north Germany, Thuringia and Silesia, the
limestones pass into the detrital culm formations, which owe their
existence to a southern uplifted massif, the complement of the
synclines already mentioned. Sediments approaching to the culm type,
with similar flora and fauna, were deposited in synclinal hollows in
parts of France and Spain.

Thus western Europe in early Carboniferous time was occupied by a
series of constricted, gulf-like seas; and on account of the steady
progress of intermittent warping movements of the crust, we find that
the areas of clearer water, in which the limestone-building organisms
could exist, were repeatedly able to spread, thus forming those thin
limestones found interbedded with shale and sandstone which occur
typically in the Yoredale district of Yorkshire and in the region to
the north, and also in the culm deposits of central Europe. The spread
of these limestones was repeatedly checked by the steady influx of
detritus from the land during the pauses in movements of depression.
Looking eastward, towards central and northern Russia, we find a wider
and much more open sea; but the continental type of deposit prevailed
in the northern portion, and here, as in Scotland, we find coal-beds
amongst the sediments (Moscow basin). Farther south in the Donetz
basin the coals only appear at the close of the Lower Carboniferous.

In North America, the crustal movements at the beginning of the period
are less evident than in Europe, but a marked parallelism exists; for
in the east, in the Appalachian tract, we find detrital sediments
prevailing, while the open sea, with great deposits of limestone, lay
out towards the west in the direction of that similar open sea which
lay towards the east of Europe and extended through Asia.

The close of the early Carboniferous period was marked by an
augmentation of the orogenic movements. The gentler synclines and
anticlines of the earlier part of the period became accentuated,
giving rise to pronounced mountain ridges, right across Europe.

This movement commenced in the central and western part of the
continent and continued throughout the whole Carboniferous period. The
mountains then formed have been called the "Palaeozoic Alps" by E.
Kayser, the "Hercynian Mountains" by M. Bertrand. The most western
range extended from Ireland through Wales and the south of England to
the central plateau of France; this was the "Armorican range" of E.
Suess. The eastern part of the chain passed from South France through
the Vosges, the Black Forest, Thuringia, Harz, the Fichtelgebirge,
Bohemia, the Sudetes, and possibly farther east; this constitutes the
"Varischen Alps" of Suess.

The sea had gained somewhat at the beginning of the Carboniferous
period in western Europe, but the effect of these movements, combined
with the rapid formation of detrital deposits from the rising land
areas, was to drive the sea steadily from the north towards the south,
until the open sea (with limestones) was relegated to what is now the
Mediterranean and to Russia and thence eastward. Similar events were
meanwhile happening in North America, for the seas were steadily
filled with sediments which drove them from the north-east towards the
south-west, and doubtless those movements which at the close of this
period uplifted the Appalachian mountains were already operative in
the same direction.

The folding of the Ural mountains began in the earlier part of this
period and was continued, after its close, into the Permian; and there
are traces of uplifts in central Asia and Armenia.

None of these movements appears to have affected the southern
hemisphere.

The net result of the erogenic movements was, that at the close of the
period there existed a great northern continental mass, embracing
Europe, North Asia and North America; and a great southern continental
mass, including South America, Africa, Australia and India. Between
these land masses lay a great Mediterranean sea--the "Tethys" of
Suess.

The conditions under which the beds of coal were formed will be found
described under that head; it will be sufficient to notice here that
some coal seams were undoubtedly formed by jungle or swamp-like
growths on the site of the deposit, and it is equally true that others
were formed by the transport and deposition of vegetable detritus. The
main point to observe in this connexion is that large tracts of land
in many parts of the world were at a critical level as regards the
sea, a condition highly favourable to frequent extensive incursions of
marine waters over the low-lying areas in a period of extreme crustal
instability.

_Vulcanicity._--In intimate relationship with the mountain-building
orogenic crustal movements was the prevalence of volcanic activity
during the earlier part of this period. In the Lower Carboniferous
rocks of Scotland intercalated volcanic rocks are strikingly abundant,
and now form an important feature in the geology of the southern
portion of that country. Of these rocks Sir Archibald Geikie says:
"Two great phases or types of volcanic action during Carboniferous
time may be recognized--(1) Plateaus, where the volcanic materials
discharged copiously from many scattered openings now form broad
tablelands or ranges of hills, sometimes many hundreds of square miles
in extent and 1500 ft. or more in thickness; (2) Puys, where the
ejections were often confined to the discharge of a small amount of
fragmentary materials from a single independent vent." The plateau
type was most extensively developed during the formation of the
Calciferous Sandstone; the puy type was of somewhat later date. Basic
lavas, with andesites, trachytes, tuffs and agglomerates are the most
common Scottish rocks of this period. Similar eruptions, but on a much
smaller scale, took place in other parts of Great Britain.

Granites, porphyries and porphyrites belonging to this period occur in
the Saxon Erzgebirge, the Harz, Thuringerwald, Vosges, Brittany,
Cornwall and Christiania. Porphyrites and tuffs are known in the
French Carboniferous. In China, at the close of the period, there were
enormous eruptions of melaphyre, porphyrite and quartz-porphyry. In
North America, the principal region of volcanic activity lay in the
west; great thicknesses of igneous rocks occur in the Lower
Carboniferous rocks of British Columbia, and from the middle of the
period until near its close volcanoes were active from Alaska to
California. Igneous rocks of this period are found also in
Australasia.

_Climate_.--That the vegetation during this period was unusually
exuberant there can be no doubt, and that a general uniformity of
climatic conditions prevailed is shown not only by the wide
distribution of coal measures, but by the uniformity of plant types
over the whole earth. It is well, however, to guard against an
over-estimation of this exuberance; it must be borne in mind that the
physiographic conditions were peculiarly favourable to the
preservation of plant remains, conditions that do not appear to have
obtained so completely in any other period. The climate, we may assume
from the distribution of land and water, was generally moist, and it
was probably mild if not warm; conditions favourable to the growth of
certain types of plants. But there is no good evidence for an excess
of carbon dioxide in the atmosphere--an assumption founded on the
luxuriance of the vegetation, coupled with the fact that vulcanicity
was active and wide-ranging. Carbon dioxide may have been present in
the air in greater abundance in earlier periods than it is at present,
but there is no reason to suppose that the percentage was appreciably
higher in the Carboniferous period than it is now.

The occurrence of _red deposits_ in western Australia, Scotland, the
Ural mountains, in Michigan, Montana and Nova Scotia, &c., associated
in some instances with the formation of gypsum and salt, clearly
points to the existence of areas of excessive evaporation, such as are
found in land-locked waters in regions where something like desert
conditions prevail. The xerophytic structures found in some of the
plants might seem to corroborate this view; but similar structures are
assumed by many plants when dwelling in brackish marshes and morasses.

The abundance of corals in some of the Carboniferous seas and possibly
also the large size of some of the Productids and foraminifera may be
taken as evidence of warm or temperate waters.

In spite of the bulk of the evidence being in favour of geniality of
climate, it is necessary to observe that certain deposits have been
recognized as glacial; in the culm of the Frankenwald, in the coal
basins of central France, and in central England, certain
conglomeratic beds have been assigned, somewhat doubtfully, to this
origin. They have also been regarded as the result of torrential
action. Glacial deposits certainly do exist in the Permo-carboniferous
formations, which are described under that head, but in the true
Carboniferous system glaciation may be taken as not proven. The
foreign boulders of granite, gneiss, &c., found in the coal-measures
of some districts, are quite as likely to have been dropped by rafts
of vegetation as to have been carried by floating icebergs.

_Economic Products._--Foremost among the useful products of the
Carboniferous rocks is the coal (_q.v._) itself; but associated with
the coal seams in Great Britain, North America and elsewhere, are very
important beds of ironstone, fire-clay, terra-cotta clay, and
occasionally oil shale and alum shale. Oil and gas are of importance
in the Lower Carboniferous Pocono sandstone of West Virginia and in
the Berea grit of Ohio, where brine also occurs.

In the Carboniferous Limestone series, the purer kinds of limestone
are used for the manufacture of lime, bleaching powder and similar
products, also as a flux in the smelting of iron; some of the less
pure varieties are used in making cement. The beds of chert are
utilized in the pottery industry, and some of the harder and more
crystalline limestones are beautiful marbles, capable of taking a high
polish.

The sandstones are used for building, and for millstones and
grindstones. Within the Carboniferous rocks, but due to the action of
various agencies long after their deposition, are important ore
formations; such are the Rio Tinto ores of Spain, the lead and zinc
ores and some haematite of the Pennine and Mendip hills and other
British localities, and many ore regions in the United States.

REFERENCES.--For a good general account of the Carboniferous system,
see A. Geikie, _Text Book of Geology_, vol. ii. (4th ed., 1903); and
for the American development see T.C. Chamberlin and R.D. Salisbury,
_Geology_, vol. ii. (1906). These two works give abundant references
to the literature of the subject. See also, _Recent Additions to
Geological Literature_, published annually by the Geological Society
of London since 1893; and _Neues Jahrbuch fur Mineralogie_
(Stuttgart). (J. A. H.)

CARBORUNDUM, a silicide of carbon formed by the action of carbon on sand (silica) at high temperatures, which on account of its great hardness is an important abrasive, and also has possible applications in the metallurgy of iron and steel. Its name was derived from _carbon_ and _corundum_ (a form of alumina), from a mistaken view as to its composition. It was first obtained accidentally in 1891 by Acheson in America, when he was experimenting with the electric furnace in the hope of producing artificial diamonds. The experiments were followed up in an incandescence furnace, which on a larger scale is now employed for the industrial manufacture of the product. A full description of the process has been given in the _Journ. Soc. Chem. Industry_, 1897, vol. xvi. p. 863. The furnace is rectangular, about 16 ft. long and 5 ft. wide by 5 ft. high, with massive brick end walls 2 ft. thick, through which are built the carbon poles, consisting of bundles of 60 parallel 3-in. carbon rods, each 3 ft. in length, with a copper rod let into the outer end to connect it with a copper cap, which in turn is connected with one of the terminals of the generating dynamo. The spaces between the carbons of the electrode are packed tightly with graphite. In preparing the furnace for use, transverse iron screens are placed temporarily across each end, the space between these and the end walls being rammed with fine coke, and that in the interior is filled to the level of the centre of the carbon poles with the charge, consisting of 34 parts of coke, with 54 of sand, 10 of sawdust and 2 of salt. A longitudinal trench is then formed in the middle, and in this is arranged a cylindrical pile of fragments of coke about 1/2 in. or more in diameter, so that they form a core, about 21 in. in diameter, connecting the carbon poles in the end walls. Temporary side walls are then built up, the iron screens are removed, and a further quantity of charge is heaped up about 3 ft. above the top of the furnace. An alternating current of about 1700 amperes at 190 volts is now switched on; as the mass becomes heated by the passage of the current the resistance diminishes, and the current is regulated until after about 2 hours or less from starting it is maintained constant at about 6000 amperes and 125 volts. Carbon monoxide is given off and burns freely around the sides and top of the furnace, tinged yellow after a time by the sodium in the salt mixed with the charge. Meanwhile a shrinkage takes place, which is made good by the addition of a further quantity of charge until the operation is complete, usually in about 36 hours from the commencement. The current is then switched off, and the side walls, after cooling for a day, are taken down, the comparatively unaltered charge from the top is removed, and the products are carefully extracted. These consist of the inner carbon core, which at the temperature of the furnace will have been for the most part converted into graphite, then a thin black crust of graphite mixed with carborundum, next a layer of nearly pure crystallized carborundum about a foot in thickness, then grey amorphous carbide of silicon mixed with increasing proportions of unaltered charge, and lastly, on the outside, the portion of the charge which had never reached the temperature necessary for reaction, and which is altered only by the intrusion of salt from the inner part of the furnace. Special precautions are taken in making and breaking the intense current here used (amounting at the end to about 750 kilowatts, or 1000 E.H.P.), a water-regulator consisting of removable iron plates dipped in salt water being used for the purpose. In such a furnace as that above described the charge weighs about 14 tons, the yield of carborundum is about 3 tons, and the expenditure of energy about 3.9 kilowatt-hours (5.2 H.P.-hours) per pound of finished product. The carborundum thus produced is crystalline, greenish, bluish or brownish in colour, sometimes opaque, but often translucent, resisting the action of even the strongest acids, and the action of air or of sulphur at high temperatures. The crude product can therefore be treated with hot sulphuric acid to purify it. In hardness it nearly equals the diamond, and it is used for tool-grinding in the form of vitrified wheels (mixed with powdered porcelain and iron, pressed into shape and fired in a kiln). Carborundum paper, made like emery paper, is now largely used in place of garnet paper in American shoe factories, and finds a market in other directions. The amorphous carbide, which was at first a waste product, has been tried, it is reported, with success as a lining for steel furnaces, as it is said not to be affected by iron or iron oxide at a white heat. (W. G. M.)

CARBOY (from the Pers. _qarabah_, a flagon), a large globular glass vessel or bottle, encased in wicker or iron-work for protection, used chiefly for holding vitriol, nitric acid and other corrosive liquids.

CARBUNCLE (Lat. _carbunculus_, diminutive of _carbo_, a glowing coal), in mineralogy, a garnet (q.v.) cut with a convex surface. In medicine the name given to an acute local inflammation of the deeper layers of the skin, followed by sloughing. It is accompanied by great local tension and by constitutional disturbance, and in the early stages the pain is often extremely acute. A hard flattened swelling of a deep-red colour is noticed on the back, face or extremities. This gradually extends until in some instances it may become as large as a dinner-plate. Towards the centre of the mass numerous small openings form on the surface, from which blood and matter escape. Through these openings a yellow slough or "core" of leathery consistence can be seen. Carbuncle is an intense local inflammation caused by septic germs which have in some manner found their way to the part. It is particularly apt to occur in persons whose health is depressed by mental worries, or by such troubles as chronic disease of the kidneys or blood-vessels, or by diabetes. The attack ends in mortification of the affected tissue, and, after much suffering, the core or mortified part slowly comes away. The modern treatment consists in cutting into the inflamed area, scraping out the germ-laden core at the earliest possible moment, and applying germicides. This method relieves the pain at once, materially diminishes the risk of blood-poisoning, and hastens convalescence. (E. O.*)

CARCAGENTE, or CARCAJENTE, a town of eastern Spain, in the province of Valencia; near the right bank of the river Jucar, at the junction between the Valencia-Murcia and Carcagente-Denia railways. Pop. (1900) 12,262. Carcagente is a picturesque town, of considerable antiquity. Various Roman remains have been found in its neighbourhood. It is surrounded by groves of orange, palm and mulberry trees, and contains many Moorish houses, whose old-fashioned blue-tiled cupolas contrast with the chimneys of the silk mills and linen factories opened in modern times. An important local industry is the cultivation of rice, for which the moist and warm climate of the low-lying Jucar valley is well suited.

CARCAR, a town of the province of Cebu, island of Cebu, Philippine Islands, on the Carcar river near its mouth at the head of Carcar Bay, 23 m. S.W. of Cebu, the capital. It is connected with Cebu by a railway, and a branch of this railway extending across the island to Barili and Dumanjug was projected in 1908. Carcar has some coast trade. The surrounding country is rugged, and produces Indian corn and sugar in considerable quantity. The language is Cebu-Visayan. Carcar was founded in 1624.

CARCASS, the dead body of an animal. As a butcher's term, the word means the body of an animal without the head, extremities and offal. It is also used of a hollow iron case filled with combustibles, and fired from a howitzer to set fire to buildings, ships, &c., the flames issuing through holes pierced in the sides. The word is common in various forms to Romanic languages, but the ultimate origin is obscure. Possible derivations are from the Lat. _caro_, flesh, and Ital. _casso_ or _cassa_, chest, or from a Med. Gr. _[Greek: tarkasion]_, a quiver, for which the Fr. is _carquois_, and Port. _carcaz_.

CARCASSONNE, a city of south-western France, capital of the department of Aude, 57 m. S.E. of Toulouse, on the Southern railway between that city and Narbonne. Pop. (1906) 25,346. Carcassonne is divided by the river Aude into two distinct towns, the Ville Basse and the Cite, which are connected by two bridges, one modern, the other dating from the 13th century. The Cite occupies the summit of an abrupt and isolated hill on the right bank of the river. Its dirty and irregular streets are inhabited by a scanty population of workpeople, and its interest lies mainly in its ancient fortifications (see FORTIFICATION AND SIEGECRAFT) which, for completeness and strength, are unique in France and probably in Europe. They consist of a double line of ramparts, of which the outer measures more than 1600 yds. in circumference. These are protected at frequent intervals by towers, and can be entered only by two gates, one to the east, the other to the west, both of which are themselves elaborately fortified (see GATE). In the interior, and to the north of the western gate, a citadel adjoins the fortifications. A portion of the inner line is attributed to the Visigoths of the 6th century; the rest, including the castle, seems to belong to the 11th or 12th century, while the outer circuit has been referred mainly to the end of the 13th. The old cathedral of St Nazaire dates from the 11th to the 14th centuries. The nave was begun in 1096 and is Romanesque in style; the transept and choir, which contain magnificent stained glass of the Renaissance period, are of Gothic architecture. Both the fortifications and the church were restored by Viollet-le-Duc between 1850 and 1880. On the left bank of the Aude, between it and the Canal du Midi, lies the new town, clean, well-built and flourishing, with streets intersecting each other at right angles. It is surrounded by boulevards occupying the site of its ramparts, and is well provided with fountains, public squares and gardens planted with fine plane-trees. The most interesting buildings are the cathedral of St Michel, dating from the 13th century but restored in modern times, and St Vincent, a church of the 14th century, remarkable for the width of its nave.

Carcassonne is the seat of a bishop, a prefect and a court of assizes, and has tribunals of first instance and of commerce, a chamber of commerce and a branch of the Bank of France. It also has a lycee for boys, training-colleges, theological seminaries, a library and a museum rich in paintings. The old cloth industry is almost extinct. The town is, however, an important wine-market, and the vineyards of the vicinity are the chief source of its prosperity, which is enhanced by its port on the Canal du Midi. Tanning and leather-dressing, distilling, the manufacture of agricultural implements, furniture and corks, cooperage and the preparation of preserved fruits, are prominent industries.

Carcassonne occupies the site of _Carcaso_, an ancient city of Gallia Narbonensis, which belonged to the Volcae Tectosages. It was a place of some importance at the time of Caesar's invasion, but makes almost no appearance in Roman history. On the disintegration of the empire, it fell into the hands of the Visigoths, who, in spite of the attacks of the Franks, especially in 585, retained possession till 724, when they were expelled by the Arabs, destined in turn to yield before long to Pippin the Short. From about 819 to 1082 Carcassonne formed a separate countship, and from the latter date till 1247 a viscountship. Towards the end of the 11th century the viscounts of Carcassonne assumed the style of viscounts of Beziers, which town and its lords they had dominated since the fall of the Carolingian empire. The viscounty of Carcassonne, together with that of Beziers, was confiscated to the crown in 1247, as a result of the part played by the viscount Raymond Roger against Simon de Montfort in the Albigensian crusade, during which in 1209 the city was taken by the Crusaders (see ALBIGENSES). A revolt of the city against the royal authority was severely punished in 1262 by the expulsion of its principal inhabitants, who were, however, permitted to take up their quarters on the other side of the river. This was the origin of the new town, which was fortified in 1347. During the religious wars, Carcassonne several times changed hands, and it did not recognize Henry IV. till 1596.

See E.E. Viollet-le-Duc, _La Cite de Carcassonne_ (Paris, 1858); L.
Fedie, _Histoire de Carcassonne_ (Carcassonne, 1887).

CARDAMOM, the fruit of several plants of the genera _Elettaria_ and _Amomum_, belonging to the natural order Zingiberaceae, the principal of which is _Elettaria Cardamomum_, from which the true officinal or Malabar cardamom is derived. The Malabar cardamom plant is a large perennial herb with a thick fleshy root-stock, which sends up flowering stems, 6 to 12 ft. high. The large leaves are arranged in two rows, have very long sheaths enveloping the stem and a lanceolate spreading blade 1 to 2-1/2 ft. long. The fruit is an ovate-triangular, three-celled, three-valved capsule (about 1/5 in. long, of a dirty yellow colour) enclosing numerous angular seeds, which form the valuable part of the plant. It is a native of the mountainous parts of the Malabar coast of India, and the fruits are procured either from wild plants or by cultivation throughout Travancore, western Mysore, and along the western Ghauts. A cardamom of much larger size found growing in Ceylon was formerly regarded as belonging to a distinct species, and described as such under the name of _Elettaria major_; but it is now known to be only a variety of the Malabar cardamom. In commerce, several varieties are distinguished according to their size and flavour. The most esteemed are known as "shorts," a name given to such capsules as are from a quarter to half an inch long and about a quarter broad. Following these come "short-longs" and "long-longs," also distinguished by their size, the largest reaching to about an inch in length. The Ceylon cardamom attains a length of an inch and a half and is about a third of an inch broad, with a brownish pericarp and a distinct aromatic odour. Among the other plants, the fruits of which pass in commerce as cardamoms, are the round or cluster cardamom, _Amomum Cardamomum_, a native of Siam and Java; the bastard cardamom of Siam, _A. xanthioides_ --the Bengal cardamom, which is the fruit of _A. subulatum_, a native of Nepal; the Java cardamom, produced by _A. maximum_; and the Korarima cardamom of Somaliland. The last-named is the product of a plant which is unknown botanically. Cardamoms generally are possessed of a pleasant aromatic odour, and an agreeable, spicy taste. On account of their flavour they are much used with other medicines, and they form a principal ingredient in curries and compounded spices. In the north of Europe they are much used as a spice and flavouring material for cakes and liqueurs; and they are very extensively employed in the East for chewing with betel, &c.

CARDAN [Ital. CARDANO], GIROLAMO [GERONYMO or HIERONIMO] (1501-1576), Italian mathematician, physician and astrologer, born at Pavia on the 24th of September 1501, was the illegitimate son of Facio Cardano (1444-1524), a learned jurist of Milan, himself distinguished by a taste for mathematics. He was educated at the university of Pavia, and subsequently at that of Padua, where he graduated in medicine. He was, however, excluded from the College of Physicians at Milan on account of his illegitimate birth, and it is not surprising that his first book should have been an exposure of the fallacies of the faculty. A fortunate cure of the child of the Milanese senator Sfondrato now brought him into notice, and the interest of his patron procured him admission into the medical body. About this time (1539) he obtained additional celebrity by the publication of his _Practica arithmeticae generalis_, a work of great merit for the time, and he became engaged in a correspondence with Niccolo Tartaglia, who had discovered a solution of cubic equations. This discovery Tartaglia had kept to himself, but he was ultimately induced to communicate it to Cardan under a solemn promise that it should never be divulged. Cardan, however, published it in his comprehensive treatise on algebra (_Artis magnae sive de regulis Algebrae liber unus_) which appeared at Nuremberg in 1545 (see ALGEBRA: _History_). Two years previously he had published a work even more highly regarded by his contemporaries, his celebrated treatise on astrology. As a believer in astrology Cardan was on a level with the best minds of his age; the distinction consisted in the comparatively cautious spirit of his inquiries and his disposition to confirm his assertions by an appeal to facts, or what he believed to be such. A very considerable part of his treatise is based upon observations carefully collected by himself, and seemingly well calculated to support his theories so far as they extend. Numerous instances of his belief in dreams and omens may be collected from his writings, and he especially valued himself on being one of the five or six celebrated men to whom, as to Socrates, had been vouchsafed the assistance of a guardian daemon.

In 1547 he was appointed professor of medicine at Pavia. The publication of his works on algebra and astrology at this juncture had gained for him a European renown, and procured him flattering offers from Pope Paul III. and the king of Denmark, both of which he declined. In 1551 his reputation was crowned by the publication of his great work, _De Subtilitate Rerum_, which embodied the soundest physical learning of his time and simultaneously represented its most advanced spirit of speculation. It was followed some years later by a similar treatise, _De Varietate Rerum_ (1557), the two making in effect but one book. A great portion of this is occupied by endeavours, commonly futile, to explain ordinary natural phenomena, but its chief interest for us consists in the hints and glimpses it affords of principles beyond the full comprehension of the writer himself, and which the world was then by no means ready to entertain. The inorganic realm of Nature he asserts to be animated no less than the organic; all creation is progressive development; all animals were originally worms; the inferior metals must be regarded as _conatus naturae_ towards the production of gold. The indefinite variability of species is implied in the remark that Nature is seldom content with a single variation from a customary type. The oviparous habits of birds are explained by their tendency to favour the perpetuation of the species, precisely in the manner of modern naturalists. Animals were not created for the use of man, but exist for their own sakes. The origin of life depends upon cosmic laws, which Cardan naturally connects with his favourite study of astrology. The physical divergencies of mankind arise from the effects of climate and the variety of human circumstances in general. Cardan's views on the dissimilarity of languages are much more philosophical than usual at his time; and his treatise altogether, though weak in particular details, is strong in its pervading sense of the unity and omnipotence of natural law, which renders it in some degree an adumbration of the course of science since the author's day. It was attacked by J.C. Scaliger, whom Cardan refuted without difficulty.

The celebrity which Cardan had acquired led in the same year (1551) to his journey to Scotland as the medical adviser of Archbishop Hamilton of St Andrews. The archbishop was supposed to be suffering from consumption, a complaint which Cardan, under a false impression, as he frankly admits, had represented himself as competent to cure. He was of great service to the archbishop, whose complaint proved to be asthmatical; but the principal interest attaching to his expedition is derived from his account of the disputes of the medical faculty at Paris, and of the court of Edward VI. of England. The Parisian doctors were disturbed by the heresies of Vesalius, who was beginning to introduce anatomical study from the human subject. Cardan's liberality of temper led him to sympathize with the innovator. His account of Edward VI.'s disposition and understanding is extremely favourable, and is entitled to credit as that of a competent observer without bias towards either side of the religious question. He cast the king's nativity, and indulged in a number of predictions which were effectually confuted by the royal youth's death in the following year.

Cardan had now attained the summit of his prosperity, and the rest of his life was little but a series of disasters. His principal misfortunes arose from the crimes and calamities of his sons, one of whom was an utter reprobate, while the tragic fate of the other overwhelmed the father with anguish. This son, Giovanni Battista, also a physician, had contracted an imprudent marriage with a girl of indifferent character, Brandonia Seroni, who subsequently proved unfaithful to him. The injured husband revenged himself with poison; the deed was detected, and the exceptional severity of the punishment seems to justify Cardan in attributing it to the rancour of his medical rivals, with whom he had never at any time been on good terms. The blow all but crushed him; his reputation and his practice waned; he addicted himself to gaming, a vice to which he had always been prone; his mind became unhinged and filled with distempered imaginations. He was ultimately banished from Milan on some accusation not specified, and although the decree was ultimately rescinded, he found it advisable to accept a professorship at Bologna (1562). While residing there in moderate comfort, and mainly occupied with the composition of supplements to his former works, he was suddenly arrested on a charge not stated, but in all probability heresy. Though he had always been careful to keep on terms with the Church, the bent of his mind had been palpably towards free thought, and the circumstance had probably attracted the attention of Pius V., who then ruled the Church in the spirit, as he had formerly exercised the functions, of an inquisitor. Through the intercession, as would appear, of some influential cardinals, Cardan was released, but was deprived of his professorship, prohibited from teaching and publishing any further, and removed to Rome, where he spent his remaining years in receipt of a pension from the pope. It seems to have been urged in his favour that his intellect had been disturbed by grief for the loss of his son--an assertion to which his frequent hallucinations lent some countenance, though the existence of any serious derangement is disproved by the lucidity and coherence of his last writings. He occupied his time at Rome in the composition of his commentaries, _De Vita Propria_, which, along with a companion treatise, _De Libris Propriis_, is our principal authority for his biography. Though he had burned much, he left behind him more than a hundred MSS., not twenty of which have been printed. He died at Rome on the 21st of September 1576.

Alike intellectually and morally, Cardan is one of the most interesting personages connected with the revival of science in Europe. He had no especial bent towards any scientific pursuit, but appears as the man of versatile ability, delighting in research for its own sake. He possessed the true scientific spirit in perfection; nothing, he tells us, among the king of France's treasures appeared to him so worthy of admiration as a certain natural curiosity which he took for the horn of a unicorn. It has been injurious to his fame to have been compelled to labour, partly in fields of research where no important discovery was then attainable, partly in those where his discoveries could only serve as the stepping-stones to others, by which they were inevitably eclipsed. His medical career serves as an illustration of the former case, and his mathematical of the latter. His medical knowledge was wholly empirical; restrained by the authority of Galen, and debarred from the practice of anatomy, nothing more could be expected than that he should stumble on some fortunate nostrums. As a mathematician, on the other hand, he effected important advances in science, but such as merely paved the way for discoveries which have obscured his own. From his astrology no results could be expected; but even here the scientific character of his mind is displayed in his common-sense treatment of what usually passed for a mystical and occult study. His prognostications are as strictly empirical as his prescriptions, and rest quite as much upon the observations which he supposed himself to have made in his practice. As frequently is the case with men incapable of rightly ordering their own lives, he is full of wisdom and sound advice for others; his ethical precepts and practical rules are frequently excellent. To complete the catalogue of his accomplishments, he is no contemptible poet.

The work of Cardan's, however, which retains most interest for this generation is his autobiography, _De Vita Propria_. In its clearness and frankness of self-revelation this book stands almost alone among records of its class. It may be compared with the autobiography of another celebrated Italian of the age, Benvenuto Cellini, but is much more free from vanity and self-consciousness, unless the extreme candour with which Cardan reveals his own errors is to be regarded as vanity in a more subtle form. The general impression is highly favourable to the writer, whose impetuosity and fits of reckless dissipation appear as mere exaggerations of the warmth of heart which imparted such strength to his domestic affections, and in the region of science imparted that passionate devotion to research which could alone have enabled him to persevere so resolutely and effect such marked advances in such multifarious fields of inquiry.

Previous Next

Comments

Encyclopaedia Britannica, 11th Edition, "Capefigue" to "Carneades"Chapter XI: Part 11

0%35 min left in chapter