Charcoal varies considerably in its properties, depending upon the particular variety of wood from which it is prepared, and also upon the process used in its manufacture. It can be made at a temperature as low as 300° C., and is then a soft, very friable material possessing a low ignition point. When made at higher temperatures it is much more dense, and its ignition point is considerably higher. Charcoal burns when heated in air, usually without the formation of flame, although a flame is apparent if the temperature be raised. It is characterized by its power of absorbing gases; thus, according to J. Hunter [Phil. Mag., 1863 (4), 25, p. 363], one volume of charcoal absorbs (at 0° C. and 760 mm. pressure) 171.7 ccs. of ammonia, 86.3 ccs. of nitrous oxide, 67.7 ccs. of carbon monoxide, 21.2 ccs. of carbon dioxide, 17.9 ccs. of oxygen, 15.2 ccs. of nitrogen, and 4.4 ccs. of hydrogen [see also J. Dewar,Ann. Chim. Phys., 1904 (8), 3, p. 5]. It also has the power of absorbing colouring matters from solution. Charcoal is used as a fuel and as a reducing agent in metallurgical processes.The element carbon unites directly with hydrogen to form acetylene when an electric arc is passed between carbon poles in an atmosphere of hydrogen (M. Berthelot); it also unites directly with fluorine, producing, chiefly, carbon tetrafluoride CF4. It burns when heated in an atmosphere of oxygen, forming carbon dioxide, and when heated in sulphur vapour it forms carbon bisulphide (q.v.). When heated with nitrogenous substances, in the presence of carbonated or caustic alkali, it forms cyanides. It combines directly with silicon, at the temperature of the electric furnace, yieldingcarborundum, SiC; and H. Moissan has also shown that it will combine with many metals at the temperature of the electric furnace, to form carbides (q.v.).The specific heat of carbon varies with the temperature the following values having been obtained by H.F. Weber (Jahresberichte, 1874, p. 63):—Diamond.Graphite.Porous wood carbon.t°.Sp. Ht.t°.Sp. Ht.t°.Sp. Ht.−50.50.0635−50.30.11380−230.1653−10.60.0955−10.70.14370−990.1935+10.70.1128+10.80.16040−2230.238585.50.176561.30.1990206.10.2733201.60.2966606.70.4408641.90.4454985.00.4589977.00.4670The atomic weight of carbon has been determined by J.B.A. Dumas and by J.S. Stas [Ann. Chim. Phys., 1841 (3), 1, p. 1:Jahresb., 1849, 223] by estimating the amount of carbon dioxide formed on burning graphite or diamond in a current of oxygen, the value obtained being 12.0 (O = 16). Confirmatory evidence has also been obtained by O.L. Erdmann and R.F. Marchand (Jour. Prak. Chem., 1841, 23, p. 159; see also F.W. Clarke,Jahresb., 1881, p. 7).Compounds.—Three oxides of carbon are known, namely, carbon suboxide, C3O2, carbon monoxide, CO, and carbon dioxide, CO2.Carbon suboxide, C3O2, is formed by the action of phosphorus pentoxide on ethyl malonate (O. Diels and B. Wolf,Ber., 1906, 39, p. 689), CH2(COOC2H5)2= 2C2H4+ 2H2O + C3O2. At ordinary temperatures it is a colourless gas, possessing a penetrating and suffocating smell. It liquefies at 7° C. It is an exceedingly reactive compound, combining with water to form malonic acid, with hydrogen chloride to form malonyl chloride, and with ammonia to form malonamide. When kept for some time in sealed tubes it changes to a yellowish liquid, from which a yellow flocculent substance gradually separates, and finally it suddenly solidifies to a dark red mass, which appears to be a polymeric form. Its vapour density agrees with the molecular formula C3O2, and this formula is also confirmed by exploding the gas with oxygen and measuring the amount of carbon dioxide produced (seeKetenes).Carbon monoxide, CO, is found to some extent in volcanic gases. It was first prepared in 1776 by J.M.F. Lassone (Mem. Acad. Paris) by heating zinc oxide with carbon, and was for some time considered to be identical with hydrogen. Cruikshank concluded that it was an oxide of carbon, a fact which was confirmed by Clement and J.B. Désormes (Ann. Chim. Phys., 1801, 38, p. 285). It may be prepared by passing carbon dioxide over red-hot carbon, or red-hot iron; by heating carbonates (magnesite, chalk, &c.) with zinc dust or iron; or by heating many metallic oxides with carbon. It may also be prepared by heating formic and oxalic acids (or their salts) with concentrated sulphuric acid (in the case of oxalic acid, an equal volume of carbon dioxide is produced); and by heating potassium ferrocyanide with a large excess of concentrated sulphuric acid, K4Fe(CN)6+ 6H2SO4+ 6H2O = 2K2SO4+ FeSO4+ 3(NH4)2SO4+ 6CO. It is a colourless, odourless gas of specific gravity 0.967 (air = 1). It is one of the most difficultly liquefiable gases, its critical temperature being −139.5° C., and its critical pressure 35.5 atmos. The liquid boils at −190° C., and solidifies at −211°C. (L.P. Cailletet,Comptes rendus, 1884, 99, p. 706). It is only very slightly soluble in water. It burns with a characteristic pale blue flame to form carbon dioxide. It is very poisonous, uniting with the haemoglobin of the blood to form carbonyl-haemoglobin. It is a powerful reducing agent, especially at high temperatures. It is rapidly absorbed by an ammoniacal or acid (hydrochloric acid) solution of cuprous chloride. It unites directly with chlorine, forming carbonyl chloride or phosgene (see below), and with nickel and iron to form nickel and iron carbonyls (seeNickelandIron). It also combines directly with potassium hydride to form potassium formate (seeFormic Acid). The volume composition of carbon monoxide is established by exploding a mixture of the gas with oxygen, two volumes of the gas combining with one volume of oxygen to form two volumes of carbon dioxide. This fact, coupled with the determination of the vapour density of the gas, establishes the molecular formula CO.Carbon dioxide, CO2, is a gas first distinguished from air by van Helmont (1577-1644), who observed that it was formed in fermentation processes and during combustion, and gave to it the namegas sylvestre. J. Black (Edin. Phys. and Lit. Essays, 1755) showed that it was a constituent of the carbonated alkalis and called it “fixed air.” T.O. Bergman, in 1774, pointed out its acid character, and A.L. Lavoisier (1781-1788) first proved it to be an oxide of carbon by burning carbon in the oxygen obtained from the decomposition of mercuric oxide. It is a regular constituent of the atmosphere, and is found in many spring waters and in volcanic gases; it also occurs in the uncombined condition at the Grotto del Cane (Naples) and in the Poison Valley (Java). It is a constituent of the minerals cerussite, malachite, azurite, spathic iron ore, calamine, strontianite, witherite, calcite aragonite, limestone, &c. It may be prepared by burning carbon in excess of air or oxygen, by the direct decomposition of many carbonates by heat, and by the decomposition of carbonateswith mineral acids, M2CO8+ 2HCl = 2MCl + H2O + CO2. It is also formed in ordinary fermentation processes, in the combustion of all carbon compounds (oil, gas, candles, coal, &c.), and in the process of respiration.It is a colourless gas, possessing a faint pungent smell and a slightly acid taste. It does not burn, and does not support ordinary combustion, but the alkali metals and magnesium, if strongly heated, will continue to burn in the gas with formation of oxides and liberation of carbon. Its specific gravity is 1.529 (air = 1). It is readily condensed, passing into the liquid condition at 0° C. under a pressure of 35 atmospheres. Its critical temperature is 31.35° C., and its critical pressure is 72.9 atmos. The liquid boils at −78.2° C. (l atmo.), and by rapid evaporation can be made to solidify to a snow-white solid which melts at −65° C.(seeLiquid Gases). Carbon dioxide is moderately soluble in water, its coefficient of solubility at 0° C. being 1.7977 (R. Bunsen). It is still more soluble in alcohol. The solution of the gas in water shows a faintly acid reaction and is supposed to containcarbonic acid, H2CO3. The gas is rapidly absorbed by solutions of the caustic alkalis, with the production of alkaline carbonates (q.v.), and it combines readily with potassium hydride to form potassium formate. It unites directly with ammonia gas to form ammonium carbamate, NH2COONH4. It may be readily recognized by the white precipitate which it forms when passed through lime or baryta water. Carbon dioxide dissociates, when strongly heated, into carbon monoxide and oxygen, the reaction being a balanced action; the extent of dissociation for varying temperatures and pressures has been calculated by H. Le Chateller (Zeit. Phys. Chem., 1888, 2, p. 782; see H. Sainte-Claire Deville,Comptes rendus, 1863, 56, p. 195 et seq.). The volume composition of carbon dioxide is determined by burning carbon in oxygen, when it is found that the volume of carbon dioxide formed is the same as that of the oxygen required for its production, hence carbon dioxide contains its own volume of oxygen. Carbon dioxide finds industrial application in the preparation of soda by the Solvay process, in the sugar industry, in the manufacture of mineral waters, and in the artificial production of ice.Carbonyl chloride(phosgene), COCl2, was first obtained by John Davy (Phil. Trans., 1812, 40, p. 220). It may be prepared by the direct union of carbon monoxide and chlorine in sunlight (Th. Wilm and G. Wischin,Ann., 1868, 14, p. 150); by the action of phosphorus pentoxide on carbon tetrachloride at 200-210° C. (G. Gustavson,Ber., 1872, 5, p. 30), 4CCl4+ P4O10= 2CO2+ 4POCl3+ 2COCl2; by the oxidation of chloroform with chromic acid mixture (A. Emmerling and B. Lengyel,Ber., 1869, 2, p. 54), 4CHCl3+ 3O2= 4COCl2+ 2H2O + 2Cl2; or most conveniently by heating carbon tetrachloride with fuming sulphuric acid (H. Erdmann,Ber., 1893, 26, p. 1993), 2SO3+ CCl4= S2O5Cl2+ COCl2.It is a colourless gas, possessing an unpleasant pungent smell. Its vapour density is 3.46 (air = 1). It may be condensed to a liquid, which boils at 8° C. It is readily soluble in benzene, glacial acetic acid, and in many hydrocarbons. Water decomposes it violently, with formation of carbon dioxide and hydrochloric acid. It reacts with alcohol to form chlorcarbonic ester and ultimately diethyl carbonate (seeCarbonates), and with ammonia it yields urea (q.v.). It is employed commercially in the production of colouring matters (seeBenzophenone), and for various synthetic processes.Carbon oxysulphide, COS, was first prepared by C. Than in 1867 (Ann. Suppl., 5, p. 236) by passing carbon monoxide and sulphur vapour through a tube at a moderate heat. It is also formed by the action of sulphuretted hydrogen on the isocyanic esters, 2CONC2H5+ H2S = COS + CO(NHC2H5)2, by the action of concentrated sulphuric acid on the isothiocyanic esters, RNCS + H2O = COS + RNH2, or of dilute sulphuric acid on the thiocyanates. In the latter reaction various other compounds, such as carbon dioxide, carbon bisulphide and hydrocyanic acid, are produced. They are removed by passing the vapours in succession through concentrated solutions of the caustic alkalis, concentrated sulphuric acid, and triethyl phosphine; the residual gas is then purified by liquefaction (W. Hempel,Zeit. angew. Chemie, 1901, 14, p. 865). It is also formed when sulphur trioxide reacts with carbon bisulphide at 100° C., CS2+ 3SO3= COS + 4SO2, and by the decomposition of ethyl potassium thiocarbonate with hydrochloric acid, CO(OC2H5)SK + HCl = COS + KCl + C2H5OH. It is a colourless, odourless gas, which burns with a blue flame and is decomposed by heat. Its vapour density is 2.1046 (air = 1). The liquefied gas boils at −47° C. under atmospheric pressure. It is soluble in water; the aqueous solution gradually decomposes on standing, forming carbon dioxide and sulphuretted hydrogen. It is easily soluble in solutions of the caustic alkalis, provided they are not too concentrated, forming solutions of alkaline carbonates and sulphides, COS + 4KHO = K2CO3+ K2S + 2H2O.
Charcoal varies considerably in its properties, depending upon the particular variety of wood from which it is prepared, and also upon the process used in its manufacture. It can be made at a temperature as low as 300° C., and is then a soft, very friable material possessing a low ignition point. When made at higher temperatures it is much more dense, and its ignition point is considerably higher. Charcoal burns when heated in air, usually without the formation of flame, although a flame is apparent if the temperature be raised. It is characterized by its power of absorbing gases; thus, according to J. Hunter [Phil. Mag., 1863 (4), 25, p. 363], one volume of charcoal absorbs (at 0° C. and 760 mm. pressure) 171.7 ccs. of ammonia, 86.3 ccs. of nitrous oxide, 67.7 ccs. of carbon monoxide, 21.2 ccs. of carbon dioxide, 17.9 ccs. of oxygen, 15.2 ccs. of nitrogen, and 4.4 ccs. of hydrogen [see also J. Dewar,Ann. Chim. Phys., 1904 (8), 3, p. 5]. It also has the power of absorbing colouring matters from solution. Charcoal is used as a fuel and as a reducing agent in metallurgical processes.
The element carbon unites directly with hydrogen to form acetylene when an electric arc is passed between carbon poles in an atmosphere of hydrogen (M. Berthelot); it also unites directly with fluorine, producing, chiefly, carbon tetrafluoride CF4. It burns when heated in an atmosphere of oxygen, forming carbon dioxide, and when heated in sulphur vapour it forms carbon bisulphide (q.v.). When heated with nitrogenous substances, in the presence of carbonated or caustic alkali, it forms cyanides. It combines directly with silicon, at the temperature of the electric furnace, yieldingcarborundum, SiC; and H. Moissan has also shown that it will combine with many metals at the temperature of the electric furnace, to form carbides (q.v.).
The specific heat of carbon varies with the temperature the following values having been obtained by H.F. Weber (Jahresberichte, 1874, p. 63):—
The atomic weight of carbon has been determined by J.B.A. Dumas and by J.S. Stas [Ann. Chim. Phys., 1841 (3), 1, p. 1:Jahresb., 1849, 223] by estimating the amount of carbon dioxide formed on burning graphite or diamond in a current of oxygen, the value obtained being 12.0 (O = 16). Confirmatory evidence has also been obtained by O.L. Erdmann and R.F. Marchand (Jour. Prak. Chem., 1841, 23, p. 159; see also F.W. Clarke,Jahresb., 1881, p. 7).
Compounds.—Three oxides of carbon are known, namely, carbon suboxide, C3O2, carbon monoxide, CO, and carbon dioxide, CO2.Carbon suboxide, C3O2, is formed by the action of phosphorus pentoxide on ethyl malonate (O. Diels and B. Wolf,Ber., 1906, 39, p. 689), CH2(COOC2H5)2= 2C2H4+ 2H2O + C3O2. At ordinary temperatures it is a colourless gas, possessing a penetrating and suffocating smell. It liquefies at 7° C. It is an exceedingly reactive compound, combining with water to form malonic acid, with hydrogen chloride to form malonyl chloride, and with ammonia to form malonamide. When kept for some time in sealed tubes it changes to a yellowish liquid, from which a yellow flocculent substance gradually separates, and finally it suddenly solidifies to a dark red mass, which appears to be a polymeric form. Its vapour density agrees with the molecular formula C3O2, and this formula is also confirmed by exploding the gas with oxygen and measuring the amount of carbon dioxide produced (seeKetenes).
Carbon monoxide, CO, is found to some extent in volcanic gases. It was first prepared in 1776 by J.M.F. Lassone (Mem. Acad. Paris) by heating zinc oxide with carbon, and was for some time considered to be identical with hydrogen. Cruikshank concluded that it was an oxide of carbon, a fact which was confirmed by Clement and J.B. Désormes (Ann. Chim. Phys., 1801, 38, p. 285). It may be prepared by passing carbon dioxide over red-hot carbon, or red-hot iron; by heating carbonates (magnesite, chalk, &c.) with zinc dust or iron; or by heating many metallic oxides with carbon. It may also be prepared by heating formic and oxalic acids (or their salts) with concentrated sulphuric acid (in the case of oxalic acid, an equal volume of carbon dioxide is produced); and by heating potassium ferrocyanide with a large excess of concentrated sulphuric acid, K4Fe(CN)6+ 6H2SO4+ 6H2O = 2K2SO4+ FeSO4+ 3(NH4)2SO4+ 6CO. It is a colourless, odourless gas of specific gravity 0.967 (air = 1). It is one of the most difficultly liquefiable gases, its critical temperature being −139.5° C., and its critical pressure 35.5 atmos. The liquid boils at −190° C., and solidifies at −211°C. (L.P. Cailletet,Comptes rendus, 1884, 99, p. 706). It is only very slightly soluble in water. It burns with a characteristic pale blue flame to form carbon dioxide. It is very poisonous, uniting with the haemoglobin of the blood to form carbonyl-haemoglobin. It is a powerful reducing agent, especially at high temperatures. It is rapidly absorbed by an ammoniacal or acid (hydrochloric acid) solution of cuprous chloride. It unites directly with chlorine, forming carbonyl chloride or phosgene (see below), and with nickel and iron to form nickel and iron carbonyls (seeNickelandIron). It also combines directly with potassium hydride to form potassium formate (seeFormic Acid). The volume composition of carbon monoxide is established by exploding a mixture of the gas with oxygen, two volumes of the gas combining with one volume of oxygen to form two volumes of carbon dioxide. This fact, coupled with the determination of the vapour density of the gas, establishes the molecular formula CO.
Carbon dioxide, CO2, is a gas first distinguished from air by van Helmont (1577-1644), who observed that it was formed in fermentation processes and during combustion, and gave to it the namegas sylvestre. J. Black (Edin. Phys. and Lit. Essays, 1755) showed that it was a constituent of the carbonated alkalis and called it “fixed air.” T.O. Bergman, in 1774, pointed out its acid character, and A.L. Lavoisier (1781-1788) first proved it to be an oxide of carbon by burning carbon in the oxygen obtained from the decomposition of mercuric oxide. It is a regular constituent of the atmosphere, and is found in many spring waters and in volcanic gases; it also occurs in the uncombined condition at the Grotto del Cane (Naples) and in the Poison Valley (Java). It is a constituent of the minerals cerussite, malachite, azurite, spathic iron ore, calamine, strontianite, witherite, calcite aragonite, limestone, &c. It may be prepared by burning carbon in excess of air or oxygen, by the direct decomposition of many carbonates by heat, and by the decomposition of carbonateswith mineral acids, M2CO8+ 2HCl = 2MCl + H2O + CO2. It is also formed in ordinary fermentation processes, in the combustion of all carbon compounds (oil, gas, candles, coal, &c.), and in the process of respiration.
It is a colourless gas, possessing a faint pungent smell and a slightly acid taste. It does not burn, and does not support ordinary combustion, but the alkali metals and magnesium, if strongly heated, will continue to burn in the gas with formation of oxides and liberation of carbon. Its specific gravity is 1.529 (air = 1). It is readily condensed, passing into the liquid condition at 0° C. under a pressure of 35 atmospheres. Its critical temperature is 31.35° C., and its critical pressure is 72.9 atmos. The liquid boils at −78.2° C. (l atmo.), and by rapid evaporation can be made to solidify to a snow-white solid which melts at −65° C.(seeLiquid Gases). Carbon dioxide is moderately soluble in water, its coefficient of solubility at 0° C. being 1.7977 (R. Bunsen). It is still more soluble in alcohol. The solution of the gas in water shows a faintly acid reaction and is supposed to containcarbonic acid, H2CO3. The gas is rapidly absorbed by solutions of the caustic alkalis, with the production of alkaline carbonates (q.v.), and it combines readily with potassium hydride to form potassium formate. It unites directly with ammonia gas to form ammonium carbamate, NH2COONH4. It may be readily recognized by the white precipitate which it forms when passed through lime or baryta water. Carbon dioxide dissociates, when strongly heated, into carbon monoxide and oxygen, the reaction being a balanced action; the extent of dissociation for varying temperatures and pressures has been calculated by H. Le Chateller (Zeit. Phys. Chem., 1888, 2, p. 782; see H. Sainte-Claire Deville,Comptes rendus, 1863, 56, p. 195 et seq.). The volume composition of carbon dioxide is determined by burning carbon in oxygen, when it is found that the volume of carbon dioxide formed is the same as that of the oxygen required for its production, hence carbon dioxide contains its own volume of oxygen. Carbon dioxide finds industrial application in the preparation of soda by the Solvay process, in the sugar industry, in the manufacture of mineral waters, and in the artificial production of ice.
Carbonyl chloride(phosgene), COCl2, was first obtained by John Davy (Phil. Trans., 1812, 40, p. 220). It may be prepared by the direct union of carbon monoxide and chlorine in sunlight (Th. Wilm and G. Wischin,Ann., 1868, 14, p. 150); by the action of phosphorus pentoxide on carbon tetrachloride at 200-210° C. (G. Gustavson,Ber., 1872, 5, p. 30), 4CCl4+ P4O10= 2CO2+ 4POCl3+ 2COCl2; by the oxidation of chloroform with chromic acid mixture (A. Emmerling and B. Lengyel,Ber., 1869, 2, p. 54), 4CHCl3+ 3O2= 4COCl2+ 2H2O + 2Cl2; or most conveniently by heating carbon tetrachloride with fuming sulphuric acid (H. Erdmann,Ber., 1893, 26, p. 1993), 2SO3+ CCl4= S2O5Cl2+ COCl2.
It is a colourless gas, possessing an unpleasant pungent smell. Its vapour density is 3.46 (air = 1). It may be condensed to a liquid, which boils at 8° C. It is readily soluble in benzene, glacial acetic acid, and in many hydrocarbons. Water decomposes it violently, with formation of carbon dioxide and hydrochloric acid. It reacts with alcohol to form chlorcarbonic ester and ultimately diethyl carbonate (seeCarbonates), and with ammonia it yields urea (q.v.). It is employed commercially in the production of colouring matters (seeBenzophenone), and for various synthetic processes.
Carbon oxysulphide, COS, was first prepared by C. Than in 1867 (Ann. Suppl., 5, p. 236) by passing carbon monoxide and sulphur vapour through a tube at a moderate heat. It is also formed by the action of sulphuretted hydrogen on the isocyanic esters, 2CONC2H5+ H2S = COS + CO(NHC2H5)2, by the action of concentrated sulphuric acid on the isothiocyanic esters, RNCS + H2O = COS + RNH2, or of dilute sulphuric acid on the thiocyanates. In the latter reaction various other compounds, such as carbon dioxide, carbon bisulphide and hydrocyanic acid, are produced. They are removed by passing the vapours in succession through concentrated solutions of the caustic alkalis, concentrated sulphuric acid, and triethyl phosphine; the residual gas is then purified by liquefaction (W. Hempel,Zeit. angew. Chemie, 1901, 14, p. 865). It is also formed when sulphur trioxide reacts with carbon bisulphide at 100° C., CS2+ 3SO3= COS + 4SO2, and by the decomposition of ethyl potassium thiocarbonate with hydrochloric acid, CO(OC2H5)SK + HCl = COS + KCl + C2H5OH. It is a colourless, odourless gas, which burns with a blue flame and is decomposed by heat. Its vapour density is 2.1046 (air = 1). The liquefied gas boils at −47° C. under atmospheric pressure. It is soluble in water; the aqueous solution gradually decomposes on standing, forming carbon dioxide and sulphuretted hydrogen. It is easily soluble in solutions of the caustic alkalis, provided they are not too concentrated, forming solutions of alkaline carbonates and sulphides, COS + 4KHO = K2CO3+ K2S + 2H2O.
CARBONADO,a name given in Brazil to a dark massive form of impure diamond, known also as “carbonate” and in trade simply as carbon. It is sometimes called black diamond. Generally it is found in small masses of irregular polyhedral form, black, brown or dark-grey in colour, with a dull resinoid lustre; and breaking with a granular fracture, paler in colour, and in some cases much resembling that of fine-grained steel. Being slightly cellular, its specific gravity is rather less than that of crystallized diamond. It is found almost exclusively in the state of Bahia in Brazil, where it occurs in thecascalhoor diamond-bearing gravel. Borneo also yields it in small quantity. Formerly of little or no value, it came into use on the introduction of Leschot’s diamond-drills, and is now extremely valuable for mounting in the steel crowns used for diamond-boring. Having no cleavage, the carbon is less liable to fracture on the rotation of the drill than is crystallized diamond. The largest piece of carbonado ever recorded was found in Bahia in 1895, and weighed 3150 carats. Pieces of large size are, however, relatively less valuable than those of moderate dimensions, since they require the expenditure of much labour in reducing them to fragments of a suitable size for mounting in the drill-heads. Ilmenite has sometimes been mistaken in the South African mines for carbonado.
(F. W. R.*)
CARBONARI(an Italian word meaning “charcoal-burners”), the name of certain secret societies of a revolutionary tendency which played an active part in the history of Italy and France early in the 19th century. Societies of a similar nature had existed in other countries and epochs, but the stories of the derivation of the Carbonari from mysterious brotherhoods of the middle ages are purely fantastic. The Carbonari were probably an offshoot of the Freemasons, from whom they differed in important particulars, and first began to assume importance in southern Italy during the Napoleonic wars. In the reign (1808-1815) of Joachim Murat a number of secret societies arose in various parts of the country with the object of freeing it from foreign rule and obtaining constitutional liberties; they were ready to support the Neapolitan Bourbons or Murat, if either had fulfilled these aspirations. Their watch-words were freedom and independence, but they were not agreed as to any particular form of government to be afterwards established. Murat’s minister of police was a certain Malghella (a Genoese), who favoured the Carbonari movement, and was indeed the instigator of all that was Italian in the king’s policy. Murat himself had at first protected the sectarians, especially when he was quarrelling with Napoleon, but later, Lord William Bentinck entered into negotiations with them from Sicily, where he represented Great Britain, through their leader Vincenzo Federici (known as Capobianco), holding out promises of a constitution for Naples similar to that which had been established in Sicily under British auspices in 1812. Some Carbonarist disorders having broken out in Calabria, Murat sent General Manhès against the rebels; the movement was ruthlessly quelled and Capobianco hanged in September 1813 (see Greco,Intorno al tentativo dei Carbonari di Citeriore Calabria nel 1813). But Malghella continued secretly to protect the Carbonari and even to organize them, so that on the return of the Bourbons in 1815 King Ferdinand IV. found his kingdom swarming with them. The society comprised nobles, officers of the army, small landlords, government officials, peasants and even priests. Its organization was both curious and mysterious, and had a fantastic ritual full of symbols taken from the Christian religion, as well as from the trade of charcoal-burning, which was extensively practised in the mountains of the Abruzzi and Calabria. A lodge was called avendita(sale), members saluted each other asbuoni cugini(good cousins), God was the “Grand Master of the Universe,” Christ the “Honorary Grand Master,” also known as “the Lamb,” and every Carbonaro was pledged to deliver the Lamb from the Wolf,i.e.tyranny. Its red, blue and black flag was the standard of revolution in Italy until substituted by the red, white and green in 1831.
When King Ferdinand felt himself securely re-established at Naples he determined to exterminate the Carbonari, and to this end his minister of police, the prince of Canosa, set up another secret society called theCalderai del Contrappeso(braziers of the counterpoise), recruited from the brigands and the dregs of the people, who committed hideous excesses against supposed Liberals, but failed to exterminate the movement. On thecontrary, Carbonarism flourished and spread to other parts of Italy, and countless lodges sprang up, their adherents comprising persons in all ranks of society, including, it is said, some of royal blood, who had patriotic sentiments and desired to see Italy free from foreigners. In Romagna the movement was taken up with enthusiasm, but it also led to a certain number of murders owing to the fiery character of the Romagnols, although its criminal record is on the whole a very small one. Among the foreigners who joined it for love of Italy was Lord Byron. The first rising actively promoted by the Carbonari was the Neapolitan revolution of 1820. Several regiments were composed entirely of persons affiliated to the society, and on the 1st of July a military mutiny broke out at Monteforte, led by two officers named Morelli and Silvati, to the cry of “God, the King and the Constitution.” The troops sent against them, under General Pepe, himself a Carbonaro, sympathized with the mutineers, and the king, being powerless to resist, granted the constitution (13th of July), which he swore on the altar to observe. But the Carbonari were unable to carry on the government, and after the separatist revolt of Sicily had broken out the king went to the congress of Laibach, and obtained from the emperor of Austria the loan of an army with which to restore the autocracy. He returned to Naples early in 1821 with 50,000 Austrians, defeated the constitutionalists under Pepe, dismissed parliament, and set to work to persecute all who had been in any way connected with the movement.
A similar movement broke out in Piedmont in March 1821. Here as in Naples the Carbonari comprised many men of rank, such as Santorre di Santarosa, Count San Marzano, Giacinto di Collegno, and Count Moffa di Lisio, all officers in the army, and they were more or less encouraged by Charles Albert, the heir-presumptive to the throne. The rising was crushed, and a number of the leaders were condemned to death or long terms of imprisonment, but most of them escaped. At Milan there was only the vaguest attempt at conspiracy; but Silvio Pellico, Maroncelli and Count Confalonieri were implicated as having invited the Piedmontese to invade Lombardy, and were condemned to pass many years in the dungeons of the Spielberg.
The French revolution of 1830 had its echo in Italy, and Carbonarism raised its head in Parma, Modena and Romagna the following year. In the papal states a society called the Sanfedisti or Bande della Santa Fede had been formed to checkmate the Carbonari, and their behaviour and character resembled those of the Calderai of Naples. In 1831 Romagna and the Marches rose in rebellion and shook off the papal yoke with astonishing ease. At Parma the duchess, having rejected the demand for a constitution, left the city and returned under Austrian protection. At Modena, Duke Francis IV., the worst of all Italian tyrants, was expelled by a Carbonarist rising, and a dictatorship was established under Biagio Nardi on the 5th of February. Francis returned with an Austrian force and hanged the conspirators, including Ciro Menotti. The Austrians occupied Romagna and restored the province to the pope, but though many arrests of Carbonari were made there were no executions. Among those implicated in the Carbonarist movement was Louis Napoleon, who even in after years, when he was ruling France as Napoleon III., never quite forgot that he had once been a conspirator, a fact which influenced his Italian policy. The Austrians retired from Romagna and the Marches in July 1831, but Carbonarism and anarchy having broken out again, they returned, while the French occupied Ancona. The Carbonari after these events ceased to have much importance, their place being taken by the more energetic Giovane Italia Society presided over by Mazzini.
In France, Carbonarism began to take root about 1820, and was more thoroughly organized than in Italy. The example of the Spanish and Italian revolutions incited the French Carbonari, and risings occurred at Belfort, Thouars, La Rochelle and other towns in 1821, which though easily quelled revealed the nature and organization of the movement. The Carbonarist lodges proved active centres of discontent until 1830, when, after contributing to the July revolution of that year, most of their members adhered to Louis Philippe’s government.
The Carbonarist movement undoubtedly played an important part in the Italian Risorgimento, and if it did not actively contribute to the wars and revolutions of 1848-49, 1859-60 and 1866, it prepared the way for those events. One of its chief merits was that it brought Italians of different classes and provinces together, and taught them to work in harmony for the overthrow of tyranny and foreign rule.
Bibliography.—Much information on the Carbonari will be found in R.M. Johnston’sNapoleonic Empire in Southern Italy(2 vols., London, 1904), which contains a full bibliography; D. Spadoni’sSette, cospirazioni, e cospiratori(Turin, 1904) is an excellent monograph;Memoirs of the Secret Societies of Southern Italy, said to be by one Bertoldi or Bartholdy (London, 1821, Ital. transl. by A.M. Cavallotti, Rome, 1904); Saint-Edme,Constitution et organisation des Carbonari, P. Colletta,Storia del Reame di Napoli(Florence, 1848); B. King,A History of Italian Unity(London, 1899), with bibliography.
Bibliography.—Much information on the Carbonari will be found in R.M. Johnston’sNapoleonic Empire in Southern Italy(2 vols., London, 1904), which contains a full bibliography; D. Spadoni’sSette, cospirazioni, e cospiratori(Turin, 1904) is an excellent monograph;Memoirs of the Secret Societies of Southern Italy, said to be by one Bertoldi or Bartholdy (London, 1821, Ital. transl. by A.M. Cavallotti, Rome, 1904); Saint-Edme,Constitution et organisation des Carbonari, P. Colletta,Storia del Reame di Napoli(Florence, 1848); B. King,A History of Italian Unity(London, 1899), with bibliography.
(L. V.*)
CARBONATES.(1) The metallic carbonates are the salts of carbonic acid, H2CO3. Many are found as minerals, the more important of such naturally occurring carbonates being cerussite (lead carbonate, PbCO3), malachite and azurite (both basic copper carbonates), calamine (zinc carbonate, ZnCO3), witherite (barium carbonate, BaCO3), strontianite (strontium carbonate, SrCO3), calcite (calcium carbonate, CaCO3), dolomite (calcium magnesium carbonate, CaCO3·MgCO3), and sodium carbonate, Na2CO3. Most metals form carbonates (aluminium and chromium are exceptions), the alkali metals yielding both acid and normal carbonates of the types MHCO3and M2CO3(M = one atom of a monovalent metal); whilst bismuth, copper and magnesium appear only to form basic carbonates. The acid carbonates of the alkali metals can be prepared by saturating an aqueous solution of the alkaline hydroxide with carbon dioxide, M·OH + CO2= MHCO3, and from these acid salts the normal salts may be obtained by gentle heating, carbon dioxide and water being produced at the same time, 2MHCO3= M2CO3+ HO2+ CO2. Most other carbonates are formed by precipitation of salts of the metals by means of alkaline carbonates. All carbonates, except those of the alkali metals and of thallium, are insoluble in water; and the majority decompose when heated strongly, carbon dioxide being liberated and a residue of an oxide of the metal left. The alkaline carbonates undergo only a very slight decomposition, even at a very bright red heat. The carbonates are decomposed by mineral acids, with formation of the corresponding salt of the acid, and liberation of carbon dioxide. Many carbonates which are insoluble in water dissolve in water containing carbon dioxide. The individual carbonates are described under the various metals.
(2) The organic carbonates are the esters of carbonic acid, H2CO3, and of the unknown ortho-carbonic acid, C(OH)4. The acid esters of carbonic acid of the type HO·CO·OR are not known in the free state, but J.B. Dumas obtained barium methyl carbonate by the action of carbon dioxide on baryta dissolved in methyl alcohol (Ann., 1840, 35, p. 283).
Potassium ethyl carbonate, KO·CO·OC2H5, is obtained in the form of pearly scales when carbon dioxide is passed into an alcoholic solution of potassium ethylate, CO2+ KOC2H5= KO·CO·OC2H5. It is not very stable, water decomposing it into alcohol and the alkaline carbonate. The normal esters may be prepared by the action of silver carbonate on the alkyl iodides, or by the action of alcohols on the chlorcarbonic esters. These normal esters are colourless, pleasant-smelling liquids, which are readily soluble in water. They show all the reactions of esters, being readily hydrolysed by caustic alkalis, and reacting with ammonia to produce carbamic esters and urea. By heating with phosphorus pentachloride an alkyl group is eliminated and a chlorcarbonic ester formed. Dimethylcarbonate, CO(OCH3)2, is a colourless liquid, which boils at 90.6° C., and is prepared by heating the methyl ester of chlorcarbonic acid with lead oxide. Diethylcarbonate, CO(OC2H5)2, is a colourless liquid, which boils at 125.8° C.; its specific gravity is 0.978 (20°) [H. Kopp]. When it is heated to 120° C. with sodium ethylate it decomposes into ethyl ether and sodium ethyl carbonate (A. Geuther,Zeit. f. Chemie, 1868).Ortho-carbonic ester, C(OC2H5)4is formed by the action of sodium ethylate on chlorpicrin (H. Bassett,Ann., 1864, 132, p. 54), CCl3NO2+ 4C2H5ONa = C(OC2H5)4+ NaNO2+ 3NaCl. It is an ethereal-smelling liquid, which boils at 158-159° C., and has a specificgravity of 0.925. When heated with ammonia it yields guanidine, and on boiling with alcoholic potash it yields potassium carbonate.Chlorcarbonic ester, Cl·CO·OC2H5, is formed by the addition of well-cooled absolute alcohol to phosgene (carbonyl chloride). It is a pungent-smelling liquid, which fumes strongly on exposure to air. It boils at 93.1°C., and has a specific gravity of 1.144 (15°C.). When heated with ammonia it yields urethane. Sodium amalgam converts it into formic acid; whilst with alcohol it yields the normal carbonic ester. It is easily broken down by many substances (aluminium chloride, zinc chloride, &c.) into ethyl chloride and carbon dioxide.Percarbonates.—Barium percarbonate, BaCO4, is obtained by passing an excess of carbon dioxide into water containing barium peroxide in suspension; it is fairly stable, and yields hydrogen peroxide when treated with acids (E. Merck,Abs. J.C.S., 1907, ii. p. 859). Sodium percarbonates of the formulae Na2CO4, Na2C2O6, Na2CO5, NaHCO4(two isomers) are obtained by the action of gaseous or solid carbon dioxide on the peroxides Na2O2, Na2O3, NaHO2(two isomers) in the presence of water at a low temperature (R. Wolffenstein and E. Peltner,Ber., 1908, 41, pp. 275, 280). Potassium percarbonate, K2C2O6, is obtained in the electrolysis of potassium carbonate at −10 to −15°.
Potassium ethyl carbonate, KO·CO·OC2H5, is obtained in the form of pearly scales when carbon dioxide is passed into an alcoholic solution of potassium ethylate, CO2+ KOC2H5= KO·CO·OC2H5. It is not very stable, water decomposing it into alcohol and the alkaline carbonate. The normal esters may be prepared by the action of silver carbonate on the alkyl iodides, or by the action of alcohols on the chlorcarbonic esters. These normal esters are colourless, pleasant-smelling liquids, which are readily soluble in water. They show all the reactions of esters, being readily hydrolysed by caustic alkalis, and reacting with ammonia to produce carbamic esters and urea. By heating with phosphorus pentachloride an alkyl group is eliminated and a chlorcarbonic ester formed. Dimethylcarbonate, CO(OCH3)2, is a colourless liquid, which boils at 90.6° C., and is prepared by heating the methyl ester of chlorcarbonic acid with lead oxide. Diethylcarbonate, CO(OC2H5)2, is a colourless liquid, which boils at 125.8° C.; its specific gravity is 0.978 (20°) [H. Kopp]. When it is heated to 120° C. with sodium ethylate it decomposes into ethyl ether and sodium ethyl carbonate (A. Geuther,Zeit. f. Chemie, 1868).
Ortho-carbonic ester, C(OC2H5)4is formed by the action of sodium ethylate on chlorpicrin (H. Bassett,Ann., 1864, 132, p. 54), CCl3NO2+ 4C2H5ONa = C(OC2H5)4+ NaNO2+ 3NaCl. It is an ethereal-smelling liquid, which boils at 158-159° C., and has a specificgravity of 0.925. When heated with ammonia it yields guanidine, and on boiling with alcoholic potash it yields potassium carbonate.
Chlorcarbonic ester, Cl·CO·OC2H5, is formed by the addition of well-cooled absolute alcohol to phosgene (carbonyl chloride). It is a pungent-smelling liquid, which fumes strongly on exposure to air. It boils at 93.1°C., and has a specific gravity of 1.144 (15°C.). When heated with ammonia it yields urethane. Sodium amalgam converts it into formic acid; whilst with alcohol it yields the normal carbonic ester. It is easily broken down by many substances (aluminium chloride, zinc chloride, &c.) into ethyl chloride and carbon dioxide.
Percarbonates.—Barium percarbonate, BaCO4, is obtained by passing an excess of carbon dioxide into water containing barium peroxide in suspension; it is fairly stable, and yields hydrogen peroxide when treated with acids (E. Merck,Abs. J.C.S., 1907, ii. p. 859). Sodium percarbonates of the formulae Na2CO4, Na2C2O6, Na2CO5, NaHCO4(two isomers) are obtained by the action of gaseous or solid carbon dioxide on the peroxides Na2O2, Na2O3, NaHO2(two isomers) in the presence of water at a low temperature (R. Wolffenstein and E. Peltner,Ber., 1908, 41, pp. 275, 280). Potassium percarbonate, K2C2O6, is obtained in the electrolysis of potassium carbonate at −10 to −15°.
CARBON BISULPHIDE,CS2, a chemical product first discovered in 1796 by W.A. Lampadius, who obtained it by heating a mixture of charcoal and pyrites. It may be more conveniently prepared by passing the vapour of sulphur over red hot charcoal, the uncondensed gases so produced being led into a tower containing plates over which a vegetable oil is allowed to flow in order to absorb any carbon bisulphide vapour, and then into a second tower containing lime, which absorbs any sulphuretted hydrogen. The crude product is very impure and possesses an offensive smell; it may be purified by forcing a fine spray of lime water through the liquid until the escaping water is quite clear, the washed bisulphide being then mixed with a little colourless oil and distilled at a low temperature. For further methods of purification see J. Singer (Journ. of Soc. Chem. Ind., 1889, p. 93), Th. Sidot (Jahresb., 1869, p. 243), E. Allary (Bull. de la Soc. Chim., 1881, 35, p. 491), E. Obach (Jour. prak. Chem., 1882 (2), 26, p. 282).
When perfectly pure, carbon bisulphide is a colourless, somewhat pleasant smelling, highly refractive liquid, of specific gravity 1.2661 (18°/4°) (J.W. Brühl) or 1.29215 (0°/4°) (T.E. Thorpe). It boils at 46.04° C. (T.E. Thorpe,Journ. Chem. Soc., 1880, 37, p. 364). Its critical temperature is 277.7° C., and its critical pressure is 78.1 atmos. (J. Dewar,Chem. News, 1885, 51, p. 27). It solidifies at about −116°C., and liquefies again at about −110°C. (K. Olszewski,Jahresb., 1883, p. 75). It is a mono-molecular liquid (W. Ramsay and J. Shields,Jour. Chem. Soc., 1893, 63, p. 1089). It is very volatile, the vapour being heavy and very inflammable. It burns with a pale blue flame to form carbon dioxide and sulphur dioxide. It is almost insoluble in water, but mixes in all proportions with absolute alcohol, ether, benzene and various oils. It is a good solvent for sulphur, phosphorus, wax, iodine, &c. It dissociates when heated to a sufficiently high temperature. A mixture of carbon bisulphide vapour and nitric oxide burns with a very intense blue-coloured flame, which is very rich in the violet or actinic rays. When heated with water in a sealed tube to 150° C. it yields carbon dioxide and sulphuretted hydrogen. Zinc and hydrochloric acid reduce it to tri-thioformaldehyde (CH2S)3(A. Girard,Comptes rendus, 1856, 43, p. 396). When passed through a red-hot tube with chlorine it yields carbon tetrachloride and sulphur chloride (H. Kolbe). Potassium, when heated, burns in the vapour of carbon bisulphide, forming potassium sulphide and liberating carbon. In contact with chlorine monoxide it forms carbonyl chloride and thionyl chloride (P. Schützenberger,Ber., 1869, 2, p. 219). When passed with carbon dioxide through a red-hot tube it yields carbon oxysulphide, COS (C. Winkler), and when passed over sodamide it yields ammonium thiocyanate. A mixture of carbon bisulphide vapour and sulphuretted hydrogen, when passed over heated copper, gives, amongst other products, some methane.
Carbon bisulphide slowly oxidizes on exposure to air, but by the action of potassium permanganate or chromic acid it is readily oxidized to carbon dioxide and sulphuric acid. By the action of aqueous alkalis, carbon bisulphide is converted into a mixture of an alkaline carbonate and an alkaline thiocarbonate (J. Berzelius,Pogg. Ann., 1825, 6, p. 444), 6KHO + 3CS2= K2CO3+ 2K2CS3+ 3H2O; on the other hand, an alcoholic solution of a caustic alkali converts it into a xanthate (A. Vogel,Jahresb.,1853, p. 643),CS2+ KHO + R·OH = H2O + RO·CS·SK.Aqueous and alcoholic solutions of ammonia convert carbon bisulphide into ammonium dithiocarbamate, which readily breaks down into ammonium thiocyanate and sulphuretted hydrogen (A.W. Hofmann),CS2+ 2NH3→ NH2·CSS·NH4→ H2S + NH4CNS.Carbon bisulphide combines with primary amines to form alkyl dithiocarbamates, which when heated lose sulphuretted hydrogen and leave a residue of a dialkyl thio-urea,CS2+ 2R·NH2→ R·NH·CSS·NH3R → CS(NHR)2+ H2S;or if the aqueous solution of the dithiocarbamate be boiled with mercuric chloride or silver nitrate solution, a mustard oil (q.v.) is formed,R·NH·CSS·NH3R + HgCl2→ Hg(R·NH·CSS)2→ 2RNCS + HgS + H2S.Carbon bisulphide is used as a solvent for caoutchouc, for extracting essential oils, as a germicide, and as an insecticide.Carbon monosulphide,CS, is formed when a silent electric discharge is passed through a mixture of carbon bisulphide vapour and hydrogen or carbon monoxide (S.M. Losanitsch and M.Z. Jovitschitsch,Ber.,1897, 30. p. 135).
Carbon bisulphide slowly oxidizes on exposure to air, but by the action of potassium permanganate or chromic acid it is readily oxidized to carbon dioxide and sulphuric acid. By the action of aqueous alkalis, carbon bisulphide is converted into a mixture of an alkaline carbonate and an alkaline thiocarbonate (J. Berzelius,Pogg. Ann., 1825, 6, p. 444), 6KHO + 3CS2= K2CO3+ 2K2CS3+ 3H2O; on the other hand, an alcoholic solution of a caustic alkali converts it into a xanthate (A. Vogel,Jahresb.,1853, p. 643),
CS2+ KHO + R·OH = H2O + RO·CS·SK.
Aqueous and alcoholic solutions of ammonia convert carbon bisulphide into ammonium dithiocarbamate, which readily breaks down into ammonium thiocyanate and sulphuretted hydrogen (A.W. Hofmann),
CS2+ 2NH3→ NH2·CSS·NH4→ H2S + NH4CNS.
Carbon bisulphide combines with primary amines to form alkyl dithiocarbamates, which when heated lose sulphuretted hydrogen and leave a residue of a dialkyl thio-urea,
CS2+ 2R·NH2→ R·NH·CSS·NH3R → CS(NHR)2+ H2S;
or if the aqueous solution of the dithiocarbamate be boiled with mercuric chloride or silver nitrate solution, a mustard oil (q.v.) is formed,
R·NH·CSS·NH3R + HgCl2→ Hg(R·NH·CSS)2→ 2RNCS + HgS + H2S.
Carbon bisulphide is used as a solvent for caoutchouc, for extracting essential oils, as a germicide, and as an insecticide.
Carbon monosulphide,CS, is formed when a silent electric discharge is passed through a mixture of carbon bisulphide vapour and hydrogen or carbon monoxide (S.M. Losanitsch and M.Z. Jovitschitsch,Ber.,1897, 30. p. 135).
CARBONDALE,a city of Lackawanna county, Pennsylvania, U.S.A., on the Lackawanna river, 16 m. N.E. of Scranton. Pop. (1890) 10,833; (1900) 13,536, of whom 2553 were foreign-born; (1910 census) 17,040. Carbondale is served by the Erie, the Delaware & Hudson (which has machine shops here), and the New York, Ontario & Western railways. The city lies near the upper end of the Lackawanna valley, and the scenery of the surrounding mountains makes it a summer resort of some importance. It has a public library, a small park, an emergency hospital and the Carbondale city private hospital. Carbondale is situated in one of the richest anthracite coal regions of the state, and its principal interest is in coal. Among its manufactures are foundry and machine shop products, sheet-iron, silk, glass, thermometers and hydrometers, bobbins and refrigerating machines. The value of the city’s factory products increased from $1,146,181 in 1900 to $2,315,695 in 1905, or 102%. The settlement of the place began in 1824 with the opening of the coal mines, and Carbondale was chartered as a city in 1851.
CARBONIC ACID,in chemistry, properly H2CO3, the acid assumed to be formed when carbon dioxide is dissolved in water; its salts are termed carbonates. The name is also given to the neutral carbon dioxide from its power of forming salts with oxides, and on account of the acid nature of its solution; and, although not systematic, this use is very common.
CARBONIFEROUS SYSTEM,in geology, the whole of the great series of stratified rocks and associated volcanic rocks which occur above the Devonian or Old Red Sandstone and below the Permian or Triassic systems, belonging to the Carboniferous period. The name was first applied by W.D. Conybeare in 1821 to the coal-bearing strata of England and Wales, including the related grits and limestones immediately beneath them. The term is a relic of that early period in the history of stratigraphy when each group of strata was supposed to be distinguished by some peculiar lithological character. In this case the carbonaceous beds—coal-seams—naturally appealed most strongly to the imagination, and the name is a good one, notwithstanding the fact that coal-seams occupy but a small fraction of the total thickness of the Carboniferous system; and although subsequent investigations have demonstrated the existence of coal in other geological formations, in none of these does it play so prominent a part. The stratified rocks of this system include marine limestones, shales and sandstones; estuarine, lagoonal and fresh-water shales, sandstones and marls with beds of coal, oil-bearing rocks, gypsum and salt.
In many parts of the world there is no sharp line of demarcation between the Devonian and the Carboniferous rocks; neither can the fossil faunas and floras be clearly separated at any well-defined line; this is true in Britain, Belgium, Russia, Westphalia and parts of North America. Again, at the summit of the Carboniferous series, both the rocks and their fossil contents merge gradually into those of the succeeding Permiansystem, as in Russia, Bohemia, the Saar region and Texas. This has led certain geologists to classify the Devonian, Carboniferous and Permian into one grand system; E. Renevier in 1874 proposed to include these three into a single “Carbonique” system, later he retained only the two latter groups. There seems to be sufficient reason, however, to maintain each of these groups as a separate system and limit the term Carboniferous (carbonifèrien) in the manner indicated above. At the same time it must be remembered that there is in India, South Africa, the Urals, in Australasia and parts of North America an important series of rocks, with a “Permo-Carboniferous” fauna, which constitutes a passage formation between the Carboniferous,sensu stricto, and Jurassic rocks.
Stratigraphy.—No assemblage of stratified rocks has received such careful and detailed examination as the Carboniferous system; consequently our knowledge of the stratigraphical sequence in isolated local areas, where the coals have been exploited, is very full.In Europe, the system is very completely developed in the British Isles, where was made the first successful attempt at a classification of its various members, although at a somewhat earlier date Omalius d’Halloy had recognized aterrain bituminifèreor coal-bearing series in the Belgian region.The area within which the Carboniferous rocks of Britain occur is sufficiently extensive to contain more than one type of the system, and thus to cast much light on the varied geographical conditions under which these rocks were accumulated. In prosecuting the study of this part of British geology it is soon discovered, and it is essential to bear in mind, that, during the Carboniferous period, the land whence the chief supplies of sediment were derived rose mainly to the north and north-west, as it seems to have done from very early geological time. While therefore the centre and south of England lay under clear water of moderate depth, the north of the country and the south of Scotland were covered by shallow water, which was continually receiving sand and mud from the adjacent northern land. Hence vertical sections of the Carboniferous formations of Britain differ greatly according to the districts in which they are taken.The Coal-Measures and Millstone Grit are usually grouped together in theUpper Carboniferous, the Carboniferous Limestone series constituting theLower Carboniferous.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.Coal Measures.Upper: Red and grey sandstones, marls and clays with occasional breccias, thin coals and limestones withSpirorbis, workable coals in the South Wales, Bristol, Somerset and Forest of Dean coalfields.Middle: Sandstones, marls, shales and the most important of the British coals.Lower: Flaggy hard sandstones (ganister), shales and thin coal seams.Millstone Grit.Grits (coarse and fine), shales, thin coal seams and occasional thin limestones. The fossil plants connect this group with the coal-measures; the marine fossils have, to some extent, a Carboniferous limestone aspect.CarboniferousLimestoneSeries.Upper black shaleswith 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 (Yoredale group) into a succession of stout limestone beds between beds of sandstone and shale, and becomes increasingly detrital in character as it is traced northwards.Lower limestone shalesof the south and centre of England with marine fossils, and the Calciferous Sandstone group of Scotland with marine, estuarine and terrestrial fossils.(SeeBernician,TuedianandAvonian.)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.Continental Type of Deposit.Marine Type of Formation.Upper CarboniferousUpperProductiveCarboniferousYounger Carboniferous limestone and theFusulinalimestone of Russia and Western North AmericaLower CarboniferousLowerProductiveCarboniferousCulm (in part)Lower Carboniferous limestone seriesWhile 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 ofthe 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.UpperCarboniferous.Coal Measures =Terrain Houiller.European Development.America.PredominantPlant Types.Ouralien = (marine type)andStephanien = (continental type)PennsylvanianFerns andAnnulariasMoscovien = (marine type)andWestphalien = (continental type)Sigillariasand CalamitesLowerCarboniferous.CarboniferousLimestone Series.Dinantien = (marine pelagic,including continentaldeposits in some areas)andCulm = (marine littoral)MississippianLycopodsIn 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 genusFusulinawas abundant in what is now Russia, China, Japan, North America;Valvulinahad a wide range, as also hadEndothyraandArchaediscus; Saccamminais 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 byLithostrotionandPhillipsastraea; common tabulate forms areChaetetes, 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 areCyathocrinus, Woodocrinus, Actinocrinus; sea-urchins,Archaeocidaris, Palaeechinus,&c., were present; while the curious extinct Blastoids, which included the groups ofPentremitidaeandCodasteridae, 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 asArchimedes.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 areSpirifer, Chonetes, Athyris, Rhynchonellids and Terebratulids,DiscinaandCrania. Some species had an almost world-wide range with only minor variations; such areProductus 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 byConulariaandBellerophon. 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 (CladoselacheandCladodus); 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 whichGinkgo bilobais 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, Sphenopterisare common genera;MegaphytonandCaulopteriswere 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 asLepidodendron(with its fruit cone calledLepidostrobus), Halonia, LepidophloiosandSigillaria, 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 asStigmaria. Sphenophyllumwas 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 calledCardiocarpus. 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 asAnthracomya, 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, Gyracanthusare characteristic genera.Frequently a temporary return of marine conditions permitted the entombment of such salt water genera asLingula, Orbiculoidea, Productusin 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 fromthe conditions of plant life. Many insects, &c., have been obtained from the coalfields of Saarbrück 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, Thüringerwald, 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 ofred depositsin 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; andNeues Jahrbuch fur Mineralogie(Stuttgart).
Stratigraphy.—No assemblage of stratified rocks has received such careful and detailed examination as the Carboniferous system; consequently our knowledge of the stratigraphical sequence in isolated local areas, where the coals have been exploited, is very full.
In Europe, the system is very completely developed in the British Isles, where was made the first successful attempt at a classification of its various members, although at a somewhat earlier date Omalius d’Halloy had recognized aterrain bituminifèreor coal-bearing series in the Belgian region.
The area within which the Carboniferous rocks of Britain occur is sufficiently extensive to contain more than one type of the system, and thus to cast much light on the varied geographical conditions under which these rocks were accumulated. In prosecuting the study of this part of British geology it is soon discovered, and it is essential to bear in mind, that, during the Carboniferous period, the land whence the chief supplies of sediment were derived rose mainly to the north and north-west, as it seems to have done from very early geological time. While therefore the centre and south of England lay under clear water of moderate depth, the north of the country and the south of Scotland were covered by shallow water, which was continually receiving sand and mud from the adjacent northern land. Hence vertical sections of the Carboniferous formations of Britain differ greatly according to the districts in which they are taken.
The Coal-Measures and Millstone Grit are usually grouped together in theUpper Carboniferous, the Carboniferous Limestone series constituting theLower Carboniferous.
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 withSpirorbis, workable coals in the South Wales, Bristol, Somerset and Forest of Dean coalfields.
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 occasional thin limestones. The fossil plants connect this group with the coal-measures; the marine fossils have, to some extent, a Carboniferous limestone aspect.
Upper black shaleswith 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 (Yoredale group) into a succession of stout limestone beds between beds of sandstone and shale, and becomes increasingly detrital in character as it is traced northwards.
Lower limestone shalesof the south and centre of England with marine fossils, and the Calciferous Sandstone group of Scotland with marine, estuarine and terrestrial fossils.
(SeeBernician,TuedianandAvonian.)
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 ofthe 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 genusFusulinawas abundant in what is now Russia, China, Japan, North America;Valvulinahad a wide range, as also hadEndothyraandArchaediscus; Saccamminais 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 byLithostrotionandPhillipsastraea; common tabulate forms areChaetetes, 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 areCyathocrinus, Woodocrinus, Actinocrinus; sea-urchins,Archaeocidaris, Palaeechinus,&c., were present; while the curious extinct Blastoids, which included the groups ofPentremitidaeandCodasteridae, 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 asArchimedes.
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 areSpirifer, Chonetes, Athyris, Rhynchonellids and Terebratulids,DiscinaandCrania. Some species had an almost world-wide range with only minor variations; such areProductus 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 byConulariaandBellerophon. 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 (CladoselacheandCladodus); 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 whichGinkgo bilobais 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, Sphenopterisare common genera;MegaphytonandCaulopteriswere 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 asLepidodendron(with its fruit cone calledLepidostrobus), Halonia, LepidophloiosandSigillaria, 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 asStigmaria. Sphenophyllumwas 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 calledCardiocarpus. 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 asAnthracomya, 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, Gyracanthusare characteristic genera.
Frequently a temporary return of marine conditions permitted the entombment of such salt water genera asLingula, Orbiculoidea, Productusin 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 fromthe conditions of plant life. Many insects, &c., have been obtained from the coalfields of Saarbrück 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, Thüringerwald, 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 ofred depositsin 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; andNeues Jahrbuch fur Mineralogie(Stuttgart).