The American Cyclopædia (1879)/Coal

The American Cyclopædia
Coal by [[Author:Leo Lesquereux (geology of), S. H. Daddow (beds of) and James Macfarlane (distribution of)|Leo Lesquereux (geology of), S. H. Daddow (beds of) and James Macfarlane (distribution of)]]

Edition of 1879. See also Coal on Wikipedia, and the disclaimer. One table needs to be formatted and to be better integrated into the text.

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COAL, a black, opaque, inflammable substance, generally hard and compact, though laminated and stratified in beds between layers forming the crust of our earth. Coal has become one of the essential elements of modern civilization; in fact, the progress of the civilization of a country is now recorded by the amount of coal obtainable and employed by the inhabitants in a given time.—Mineral coal is a compound especially of carbon or of decomposed woody matter, with inflammable substances and hydrogen and oxygen gases. According to the different proportions of the volatile matter, in common language inaccurately called bitumen, the coal has a somewhat different aspect, flames more or less rapidly and actively, and develops heat in different degrees. These differences have served as a basis for a kind of classification of the coals, which, though scarcely limitable in its divisions, is generally admitted for common use. The more essential of these divisions are the following: 1. Anthracite or glance coal, a very hard, compact, lustrous, grayish black mineral, breaking in conchoidal fracture, though still bearing evidence of its original lamination. It burns slowly, with little or scarcely any flame, producing a high degree of heat. On account of the minute proportion of volatile matter in its composition, the coal is also called non-bituminous. When this coal is somewhat less dense, and has an increasing amount of volatile matter, it burns with more flame, and is then semi-anthracite. 2. Bituminous coal, though still hard, breaks more easily and more irregularly, often dividing into large cubic pieces in the plane of stratification and by cleavage. It is generally quite black, still with some lustre, contains less carbon with a larger proportion of inflammable substances than anthracite, and therefore takes fire more easily and rapidly, and burns with a bright yellow flame, developing less heat. The amount of volatile combustible matter in its composition is extremely variable, and therefore its appreciable characters, either in its value as a combustible material or in its appearance, vary in the same degree, considerably blending the classification and multiplying its names. With a moderate proportion of inflammable gases it is dry coal; with more bitumen it becomes fat coal, which passes to caking coal when in burning the matter softens and coalesces like paste. Of the moderately bituminous coals, the best known in America is called semi-bituminous, of which very large quantities are produced from the Cumberland district of Maryland, and the Broad Top, Clearfield, and Blossburg districts of Pennsylvania, along the S. E. margin of the Alleghany coal field. Of the more highly bituminous coals the most valuable is the splint or block coal of N. W. Pennsylvania, Ohio, and Indiana, which owing to its peculiar structure can be used in its raw state in the blast furnace. 3. Cannel coal is also a kind of bituminous coal. It differs much from the numerous other varieties by its fine, equal, compact, homogeneous texture, resembling a dusky black paste hardened to a mineral substance or to stone. It breaks therefore with a conchoidal fracture, and is at once distinguished from the other kinds of bituminous coal by its equal, non-laminated structure, or the absence of those horizontal thin layers which in the common kinds of bituminous coal are seen alternating in different degrees of lustre and apparent density. By distillation it yields a larger proportion of mineral oil than any other coal. Sometimes it is so highly bituminous, as in the case of the Breckinridge coal in Kentucky, that it is dangerous to use it in steamboats, or in grates through which the oil percolates when inflamed. It burns like candles, and hence its name.


 No.  NAME AND LOCALITY.  Density.   Free Carbon.   Total Carbon.   Hydrogen.   Oxygen.   Water.  Ash.

1  Peat, general .... .... 28.09 5.93 30.37  30.05  5.62
2  Lignite, Rocky Mts. 1.230 24.00 64.99 3.76 16.42  10.56  5.27
3  Anthracite, Rocky Mts. 1.300 ? 74.37 2.58 10.00  5.20 7.88
4  Cannel coal, W. Va. 1.300 23.00 82.00 5.16 8.04 2.25 2.55
5  Block coal, Penn., W. Va., O., Ind.  1.275 *30.00  82.92 6.09 10.00  2.00 1.49
Caking coal, general
Caking coal, rich gas
*15.00  85.90 5.46 5.00 2.00 1.64
25.00 84.00 6.00 5.00 3.00 2.00
7  Hard anthracite, Penn. 1.550 ? 94.00  .40 1.26 2.30 2.50
8  Soft anthracite, Penn. 1.450 ? 87.00 2.50 3.50 2.00 4.00
9  Dense anthracite, New England 1.780 .... 80.00 .... .... 10.00   10.00  

—If the more marked characters which indicate the several species of mineral coal are easily recognized at first sight, and if everybody knows the bituminous coal from the anthracite or the cannel, it is not the less certain that, considering the matter in itself and in its compounds, coal is an indivisible whole. Not only have all the kinds of coal the same constituent chemical elements, merely varying in proportion in a slight degree, but all the varieties of coal, of bituminous especially, are found in some localities in the same vein. Anthracite passes to semi-anthracite, and this to bituminous coal, by inappreciable degrees. The coal beds of Shamokin and Trevorton in Pennsylvania give anthracite and semi-anthracite. The Spadra coal of Arkansas is semi-anthracite at one place and bituminous at another. In Kentucky some veins have one half of their thickness bituminous, the other half cannel; or at other localities, as for example on the Louisa river, the miners work bituminous laminated coal at one end of a gangway and cannel at the other, and this in the whole thickness of the bed. The analysis of caking coal fails to show any difference even in the proportion of the constituent elements from that of some kinds of dry or non-caking coal. Indeed, the character of the coal, where closely examined, is constantly variable in the same bed at the same mine, even upon the same square foot of matter, as recognized from specimens when taken at the same place from the roof to the bottom of the bank, although little or no difference is observed in a large quantity as it comes from the mine.



 Albert coal, New Brunswick  1.129 61.74 36.04  2.22
 Boghead cannel (Scotch) .... 66.35 30.88  2.77
 Grayson, Ky., “jet cannel” .... 61.95 30.07  7.98
 Grayson, Ky.,  cannel 1.371 62.03 14.36 23.62
 Breckenridgen, Ky., cannel  1.150 64.30 27.16  8.48
 Torbane hill cannel 1.189 67.11 10.52 21.00
 Boghead black cannel 1.218 62.70  9.25 26.50
 Boghead brown cannel 1.160 71.06  7.10 26.20
 Hardie's (Scotch cannel)  1.420  53.70  4.90  38.80 


Constituents.   Anthracite.   Caking 
 Cherry or 
 Block coal. 

Carbon 92.56   87.952   83.025   82.924   75.25  64.00 
Hydrogen  3.33 5.239 5.250 5.491 5.50 5.00
Nitrogen  ? ? ? ? 1.61 ?
Oxygen 2.53 3.806 8.566 8.847 13.83  26.00 
Ash 1.58 1.393 1.549 1.128 2.81 4.00

In order to understand more easily the distribution of the combustible minerals, especially coal, it is convenient to have for reference a tabular section of the American geological divisions from the earliest times till now, as they have been recognized by science. The following brief review of the formations, from the lowest or oldest to those of our own time, has special reference to such evidence as they show of coal or any combustible mineral resembling it.—No trace of remains of either plants or animals has been positively recognized in the lowest formations of the earth, which, composed generally, at least, of crystalline metamorphic rocks, are considered as the result of the cooling of the surface of our planet, which was originally in a state of fusion or of vapor. The archæan rocks, also called primitive rocks, are therefore the only ones universally formed, all the others depending upon local abrasions for their materials, which, transported and deposited mostly by water, are local in their distribution. Animal life is now, and must have been from the beginning, dependent upon vegetable life as the only source of its food. The first traces of organic remains should for this reason represent plants. The primitive or archæan formations have deposits of graphite or plumbago, a matter essentially composed of carbon. It is not known as yet how this matter has been produced or whence it is derived. It has been and may be ascribed to vegetable and animal life, represented at its beginning by beings of very simple soft texture, like the confervoidal filaments which at our time live in thermal springs, filling basins of water of the temperature of the boiling point mixed with animalcules or infusoria. The remains of these plants and animals could not have been preserved, or at least could not be discovered, in the crystalline matter of the primitive rocks. The presence of graphite in the carboniferous strata of Rhode Island, and the close likeness of some beds of anthracite of this basin, which in some of its veins is scarcely distinguishable from graphite, point to vegetables for the origin of this substance. For even the hardest layers of anthracite or graphite of Rhode Island bear well preserved remains of plants of the carboniferous period, and evidently their carbon has been derived from vegetable life. The graphite of the primitive rocks, however, like the crystalline matter, granite, mica, hornblende, syenite, &c., may be due to some as yet unknown combinations of the primitive matter of our globe. The primordial or Cambrian period is subdivided into two epochs: the upper, called the Potsdam, and the lower, the Acadian epoch. In this last formation the first remains demonstrating vegetable life appear in some fucoids or marine plants of undefined forms. They become more numerous and more distinct in the Potsdam sandstone, in which large species of algæ have been obtained and described. Their size indicates already a high degree of organized life. In the Canadian period, especially in the calciferous limestone which constitutes its lowest division, these fucoidal remains increase in abundance, representing many more species, and the rocks where the remains are imbedded are often discolored by what appears to be an impregnation of mineral oil. The matter is however very sparingly distributed. But in the Trenton period, from its lowest division, the Trenton limestone, to the Cincinnati, its upper epoch, the marine vegetation is evidenced not only in an abundance of petrified plants, but in local deposits of mineral oil, especially found in connection with a predominance of fucoidal remains, which thus attest one of the wise purposes of their life in the great plan of nature. The Hudson shales give mineral oil sparingly; the Cincinnati limestone has yielded it abundantly; the black Utica shale of the same period has sometimes from 12 to 20 per cent. of mineral oil; but no trace of coal has been found in the rocks of the Trenton period. The three divisions of the Niagara period, the Niagara, the Clinton, and the Medina, have also, in their shales, limestones, and sandstones, a prodigious abundance, in some localities at least, of marine plants. In Pennsylvania the Clinton ferruginous red shale is covered over wide surfaces with these kinds of vegetable remains, together with a proportionate number of remains of


English equivalents. Pennsylvania. Nomenclature. Maximum and
New York. Missouri and Illinois. Maximum and
Kansas and Colorado. Maximum and

NEOZOIC. Recent.
 Drift, &c. ?  Pennsylvania  Penn. and N. York ?  Drift, &c. 150 ?
 Tertiary  Absent ?  Tertiary, no coal 200  Tertiary coal
 Cretaceous  Absent ?  Absent 0  Cretaceous
 Oölitic  Absent  Absent  Absent 0  Oölitic
 Triassic  Absent  Absent?  Absent 0  Triassic
 Permian  New red sandstone  New red sandstone  Absent? 0  Permian

250 to 1,500 250 to 1,000 ? 800 to 500 1,000 to 1,500

Containing lignite coal beds. Limestones and red sandstones. Richmond, Va., coal. Not investigated in the west. Containing gypsum, marls, &c., in Kansas and Colorado. Magnesian limestone.



Coal measures Millstone grit Carboniferous limestones Sub-carboniferous

Coal measures Conglomerate Red shales White sandstones


500 to 8,000 100 to 1,500 0 to 2,000 200 to 2,000

Absent Absent Absent Gray and white sandstones

Coal measures Millstone grit Carboniferous limestones

1,000 to 8,000 10 to 100 150 to 750

Concealed in Colorado by the tertiary. Occasionally seen in Colorado and Dakota.


Old red sandstone. Eifel Eifel Ludlow

Red sandstones Limestones and shales Bituminous black slates Slates and sandstones


0 to 5,000 1,000 to 7,000 600 to 1,000 100 to 1,500

Catskill Chemung, Genesee, &c. Corniferous, Onondaga, &c. Oriskansy, sandtone, &c.

Bituminous slates, shales and limestones Oriskany

300 to 500 0 to 50

Not seen


Concealed or wanting in the far west.

U. Silurian

Wenlock Caradoc

Marls, shales and limestones Medina sandstones

V. IV.

1,000 to 4,000 200 to 2,500

Saliferous, Niagara, &c. Medina sandstone, &c.

300 to 700 ?

Not seen


Concealed by tertiary in Colorado.


Bala rocks Festiniog group Lingula flags

Slates and limestones Limestones Slates and Potsdam sandstone


500 to 2,500 1,000 to 6,000 1,000 to 4,000

Slates and limestones Limestones Calciferous Potsdam sandstone

Galena and magnesian limestones and calciferous sandstones Potsdam sandstone

300 to 1,000 100 to 250

Galena and magnesian limestone Potsdam sandstone

? 50 to 250

Occasionally seen in Colorado and Dakota, but generally concealed by the tertiary, &c.





5,000 to 10,000

Huronian gneissic

(Ozark) gneissic

500 to 1,000

(Rocky Mts.) gneissic

Metalliferous group of the Rocky mountains. marine animals, attesting the dependence of animal upon vegetable life, or at least their relation to it. Rich deposits of mineral oil are found also in the rocks of this period, especially in the Niagara limestone. At Chicago, for example, this rock is completely saturated with oil. The Salina and lower Helderberg periods are generally composed of deep marine formations, where of course remains of plants are very rare, as seaweeds do not live at a great depth. Even the Salina formations have few animal remains. But the last period of the Silurian formation, the Oriskany, manifests its vegetable life not only by remains of marine plants, but near its upper part by the first traces of land vegetation, recognized in fragments of a species referable to the lycopods or club-moss family, and similar in size at least to the ground pine of our woods, lycopodium selago and L. lucidulum. They are the earliest representatives as yet known of a family of plants to which belong the genera lepidodendron, sigillaria, &c., which come later, and, by the great number of their species and the enormous size of the trees generally representing them, are called to play at a subsequent period a remarkable part in the formation of coal. From the beginning of the Devonian, the corniferous, vegetable remains appear in the strata in a far greater abundance, especially those of marine plants, together with a proportionately increased supply of mineral oil. It is the epoch of the cauda-galli grit, so called from the distribution in the rocks of a large fucoid which covers with its debris wide surfaces of shales and fills strata of great thickness. This plant passes up through the whole Devonian to the base of the carboniferous. The bitumen has been during this period treasured in large crevices of the rocks, in cavities wherefrom it is now pumped out and utilized. The oil wells of Canada come from deposits in the cauda-galli formation; in New York the cavities of the corniferous limestone, even those which have been formed by the decomposition or destruction of fossil remains, are filled with mineral oil. Above the corniferous, the black shales, the Marcellus and Genesee shale of the Hamilton period, are everywhere impregnated with bitumen, from which they receive their black color. The combustible matter is abundant enough to percolate through the fissure with water; it is also obtained from the shale by distillation. Even these black shales have been used for fuel, giving a bright flame, though they do not consume. They have been constantly searched for coal; but no coal has been found in this formation, which from its fossils is evidently of marine origin. With the bones and teeth of large fishes, it has also the remains of seaweeds to which its bituminization is due. Some scattered trunks, of conifers especially, and mostly silicified, have been dug out of the black shales of the Hamilton period. They seem to have been floated and deposited along low shores by the waves or the current of the sea. In a few localities in Canada ferns and other plants have been observed seemingly deposited in place. But nowhere has the land vegetation been luxuriant enough to produce coal, though the genera, if not the species, represented by these plants are closely allied to those of the carboniferous period. The upper Devonian, especially the Chemung, presents by its vegetable remains the same character as those of the former period; but the land vegetation becomes more and more predominant, yet not enough to produce coal. Moreover, most of the upper Devonian strata represent beach formations by their red shales. These formations have a distinct flora, far different in its typical characters from that which is recognized in the composition of coal. These extensive mud beds washed by the tides, alternately above and under water, were preparing a solid basis for the land, or a ground for the remarkable period which was to follow.—The carboniferous period, as the word implies, is essentially that of the coal formation. Its lowest part, the subcarboniferous, is its foundation, laid upon the mud beds of the Devonian. In the east of the North American basins, it is composed of thick strata of hard red shale and sandy rocks; in the west, of beds of hard compact limestone and sandstone, overlaid by the successive stages of the carboniferous in a thickness of 2,000 to 3,000 ft. From the base of the subcarboniferous measures, the land plants already in abundance appear, in ascending, in a constantly increasing proportion, while the marine plants disappear in the same degree. The composition of the first or of the lowest bed of coal indicates only the remains of land plants, which henceforth, in the whole thickness of the coal formations, constitute the vegetation; at least no remains of marine plants have been found in connection with the coal, or appear to have contributed to its composition. From the millstone grit to the Permian, the shales are mostly covered and filled with fragments of plants, which without exception belong to the species of the coal or land flora; and in some beds of sandstone also we find local deposits of trunks now silicified or petrified, all representing species of ferns, lepidodendron, sigillaria, catamites, &c., to which the coal plants are referable. The first coal beds appear in the upper part of the subcarboniferous, or somewhat lower, a short distance below the millstone grit, a formation composed of sand and pebbles agglomerated, and for this reason named conglomerate, which generally underlies the productive measures as well in Europe as in America. Under the millstone grit a few beds of coal have been formed locally, two, rarely three, not of great thickness nor of wide extent, sometimes merely in pockets, as they are called, the matter transformed into coal having filled deep hollows of an irregular bottom and of small area. In Arkansas, however, the whole coal-bearing measures are under the millstone grit, and generally contain two beds of coal, even sometimes three of wide extent, and varying in thickness from 1 to 4 ft. In eastern Kentucky and Tennessee, also in Indiana, two lower coal beds 2 to 3 ft. thick are found under the conglomerate, in near proximity to its base; and in Illinois a lowest bed of coal has been observed under the Chester limestone, an upper division of the great limestone formation which there underlies the coal measures. Coal is found in Nova Scotia, in Scotland, and in Russia also below the millstone grit. But it is only from the millstone grit upward, and in a thickness of 300 to 1,000 ft. of measures, according to the localities, that coal beds are formed of great thickness and of wide extent. The second bed of coal above the conglomerate (B) is generally composed of two or three different beds, either united in one or separated by beds of shale or even of sandstone. This bed is found over nearly the whole extent of the coal measures from Missouri to eastern Pennsylvania, and even to Massachusetts and Rhode Island. Its thickness is rarely under 3 ft., more generally 6 to 7 ft.; at Straitsville in Ohio it is 12 ft.; it is 30 ft. or more in some localities of the anthracite basin of Pennsylvania. From the millstone grit upward, in a thickness of from 500 to nearly 1,000 ft., coal beds are formed of various thickness and extent, alternating with strata of shale, limestone, sandstone, &c., up to the great Pittsburgh coal, which is, near the end of the productive carboniferous formation, what the big vein is near its beginning. The Pittsburgh bed covers, in Pennsylvania, Virginia, and Ohio, an area estimated at 20,000 sq. m., preserving generally a thickness of 4 to 6 ft., and often greater. Between the millstone grit and the Pittsburgh coal, five to twelve veins are generally found in the measures. Of course the productiveness of the measures is locally very variable. It is at its utmost in the anthracite region of Pennsylvania. At Plymouth, near Wilkesbarre, for example, where the big vein is 30 ft. thick, a section of 300 ft. of measures has 50 ft. of coal in five veins. At Scranton a section of 350 ft. indicates 60 ft. of coal in eight or nine beds. Here the largest vein is 14 ft. In the same region a section of 800 ft. has nearly 70 ft. of coal distributed in 15 beds. In the bituminous coal region of Pennsylvania and Ohio, as well as in the coal basin of Indiana and Illinois, the thickness and number of the beds of coal are somewhat reduced, as is also the thickness of the measures; but there is a remarkable relation between the formation of the coal beds and that of the intermediate strata. In the north at least, or with the exception of the Virginia coal fields, the relation indicated above is, with little difference, as one foot of coal in 18 to 22 ft. of measures; or in 500 ft. of coal measures there is generally an average thickness of 25 ft. of coal, distributed of course in several beds of various thickness. From the Pittsburgh coal above and for nearly 1,000 ft. of measures the productiveness of the carboniferous formation diminishes in such a way that, though several coal beds have been observed, they have scarcely been found anywhere of a workable thickness. The reverse of the fact remarked in the subcarboniferous, where as the land plants become more numerous the deposits of coal also increase, is seen in passing higher up above the Pittsburgh coal to the end of the carboniferous. The plants which by their components and their great size contributed most to the formation of the coal, the lepidodendron, sigillaria, &c., decrease in numbers and even disappear. Several species of the carboniferous period are seen still persisting later, even in the Permian epoch; but these species are merely ferns and calamites, which, though large and abundant enough, do not seem to have formed any dense agglomerations of woody material, like those which evidently covered the surface of the earth when the vegetation was in its full vigor.—The strata intermediate to the beds of coal are composed of sandstone, sometimes hard enough to be cut in blocks and used for building, sometimes soft and passing to shale; of limestone, iron ore, clay, and bituminous shale. Most of the coal beds rest upon a bottom of grayish or whitish soft clay, generally mixed with remains of the stigmaria, a floating plant, the most common in the coal measures, which seems to have entered largely into the composition of the clay and of some kinds of coal. The bottom clay varies in thickness from a few inches to more than 30 ft. When penetrated by ferruginous solutions, it becomes reddish, and is sometimes hardened to such a degree that it resembles limestone and breaks under the hammer like hard rock. It is the rotten limestone of the miners. Very rarely the coal beds are in immediate superposition to sandstone; none have been seen as yet upon limestone without an intermediate bed of clay. In most cases, as a coal bed becomes at its base mixed with clay which at the point of contact is black, hard, and bituminous, it passes at its upper surface into black bituminous shale or slate differently composed from that of the bottom, laminated like the coal, or in thin layers and mixed with remains of the plants which have entered into the composition of the coal. These shales, however, do not always occur, and therefore the roof of the coal is often, sandstone, or more rarely limestone. With the remains of plants, the roof shales have also fossil shells, bones, or teeth of fishes. The limestone beds of the coal have rarely if ever remains of plants, but often a great quantity of animal remains, coral, crinoids, fishes, and especially shells. As will be seen hereafter, the distribution of all these kinds of strata is normal and explainable, as is also the formation of the shales, which are seen not only as the roof of the coal beds, but interlying them, and unfortunately sometimes in numerous alternate layers with which the pure coal is so closely mixed that these coal strata are not workable. It is to the increasing thickness of these interlying clay partings, as they are named by the miners, that the subdivision of the coal beds is mainly due. Frequently coal beds are seen in one bulk at one place, and in another, divided into two by a clay parting, which by and by thickens to 10 or 20 ft. or more, and thus separates the coal into two distinct beds.—As remarked above, the Permian, at least in America, has no coal. The characters of this formation are somewhat similar in the nature of the rock to those of the subcarboniferous, mainly consisting of red shale, limestone, and sandstone. With some species of ferns of the coal measures, its flora is represented by large calamites, a genus whose species have the texture and outside form of the horsetail plants of our time, but of an immense size, and especially with new types of conifers. In North America the Permian formations are mostly composed of thick strata of magnesian limestone, overlying the upper coal measures of the west, near and along the Missouri river, especially in Kansas, and also in the Rocky mountains, where it generally underlies the cretaceous formation. The triassic period, in ascending, follows the Permian. It is represented in North America, especially in Nova Scotia, Connecticut, New Jersey, and Pennsylvania, by deposits of red hard shale with few fossil remains, and in North Carolina and Virginia by the same kind of rocks, containing however beds of combustible mineral or of coal. The coal of Richmond, that of Deep river and Dan river, is worked out of beds 4 to 6 ft. thick, and is reported to be of good quality. In connection with the coal strata, and in their roof shales, remains of fossil plants are found in profusion, indeed in the same position and in the same abundance as the remains of plants are seen in the true coal measures; but they represent far different species. With some ferns of a peculiar type, the fossil plants of the trias are mainly species of conifers, and in the greatest proportion species of cycadeæ, a family which is predominant also in the flora of the Jurassic period. Of this period, which in Europe is a formation of immense thickness, we have little in America. If has been recognized in the Rocky mountains in some beds of limestone. In one of its divisions, the oölitic, it has some fine deposits of coal in England. These beds, like all the coal beds, are overlaid by black shale imbedding vegetable remains, which mostly represent species of cycadeæ and of ferns.—Over the Jurassic we find the cretataceous. Like those of the upper Devonian, the subcarboniferous, and the Permian, its strata are mostly marine and submarine (beach formations), denoting an epoch of subsidence to prepare, after the destruction of ancient races of plants and animals, a new organic world by great changes in the atmospheric and surface circumstances of the earth. Formations of this kind have no coal. Their vegetable remains are mostly marine, and in the cretaceous they are locally present in connection with strata impregnated with bitumen. This is the case in California. The cretaceous formations of North America are extensive, and are distributed from the upper Missouri to the base of the Rocky mountains, where their thickness reaches 2,000 to 3,000 ft. The lower part, that which has been named the Dakota group from its predominance in that territory, is composed of red shale, and is evidently a beach formation immediately overlying the Permian. Though this group has no coal, but merely thin streaks of black bituminous shale, it is remarkable for its remains of fossil plants, which most of all represent dicotyledonous species. As high as the base of the cretaceous no plants of this vegetable division have been recognized. From the first appearance of land plants at the base of the Devonian, up to the cretaceous, all the species represented by their remains are referable to cryptogams and gymnosperms, these comprising the cycads and the conifers. But all at once in this Dakota group, which in America is the lowest cretaceous, we find an abundance of leaves of dicotyledonous species, sassafras, sycamore, oak, tulip tree, &c., without any remains of the former precedent and prominent types. From the Dakota group upward there is a succession of cretaceous sandstone and black shale, whose fossils are all animals, mostly large shells of species indicating a deep marine formation; and upon this a succession of thick beds of coarse hard sandstone, somewhat similar by its compounds to the millstone grit of the carboniferous, containing, especially in the intermediate layers of shale, a great abundance of fucoids and broken fragments of wood, stems, &c., appearing as brought up and mixed with the sand of the shores by the waves.—Further west, and along the eastern base of the Rocky mountains, this sandstone formation is the lowest stage of the tertiary period. It points by its compounds to the slow upheaval of a new land, and opens a new epoch where the conditions for the production of coal appear nearly as favorable as they were during the period of the true or old carboniferous formation. Along the base of the Rocky mountains, and in the high valleys of the interior of the chain, from the Rio Grande in New Mexico along the Pacific slope to Alaska, coal beds of the lower tertiary cover wide areas, and are sometimes of great thickness. In Colorado the veins now actively worked vary in thickness from 4 to 15 ft. At Evanston, Utah, the main coal, interlaid with bands of slate, is 26 ft. thick. The succession of the strata and their distribution is also remarkably similar to that of the carboniferous measures. At Marshall's, for example, in Colorado, an exposed section of 450 ft. of measures indicates 60 ft. of coal distributed in nine or ten veins, the lowest 14 ft. thick, separated by strata of sandstone, iron ore, clay, shale, &c., as are the coal beds of the carboniferous measures. Here also most of the beds of coal, if not all, are underlaid by soft white or gray clay, sometimes pure and used for pottery, like the clay of the carboniferous, sometimes dark-colored by heaped fragments of radicles of water plants. The shale and sandstone strata generally contain a profusion of remains of land plants, whose characters, related to this period, are far different from those of the carboniferous. They mostly represent palms with dicotyledonous species, oak, poplar, walnut, hickory, magnolia, cinnamon, &c. The flora of these tertiary measures of North America has afforded already many hundred species of fossil plants.—The combustible matter or the tertiary coal, often called lignite, is in its aspect scarcely distinguishable from true coal. At some localities, especially in the upper part of the measures, it is softer and more easily broken; but at others the matter is hard, compact, distinctly laminated in thin alternate layers of crystalline and more opaque matter, gives much heat by combustion, the best kinds in some localities, as at San Pete in Utah, even producing good coke, and when the beds are in proximity to upraised dikes of basalt or lava the coal is transformed into anthracite. Nothing then distinguishes this tertiary lignite from true coal but a less proportion of carbon in its compounds, and this can be recognized by chemical analysis only. The constituents are the same; only in the lignitic coal the decomposition is not as far advanced, as will be seen by comparing the analyses of the different combustible materials. In the upper tertiary, beds of lignite coal are still found, but they are less predominant, diminishing in number and thickness and in the extent of the area which they cover. The materials also in ascending gradually appear in a less advanced stage of decomposition.—In Europe lignite beds of the upper tertiary represent mere deposits of wood, especially trunks of trees transformed into a black soft substance, which preserve still the vegetable forms and also the texture of the wood, as well as if the trees had been recently cut. Later still, or rather nearer to our present epoch, the composition of the beds of lignite becomes undistinguishable from peat. To complete the similarity, old peat beds, as is especially the case in Holland, are found under thick strata of clay or sand, in two or more successive stages, or under thick gravel deposits of the drift of the quaternary. The material is mere soft peat, which by drying becomes hard as stone, and a combustible nearly as good as lignitic coal. Along the Ohio river and at various places in Ohio, Indiana, Illinois, &c., we find thick peat deposits in the clay of the drift. The bottom of the bed is clay; the combustible matter is true peat; the beds overlying it are generally hardened clay wherein leaves, nuts, acorns, &c., are found, most of these vegetable remains being already carbonized or hard and black as coal, as in the roof shale of the coal measures. In some localities trunks and branches of trees are imbedded in these clay formations; the woody substance of these vegetable remains is already softened and decomposed, and its place taken by the infiltration of clayey matter. They only need the hardening done by time to become fossilized trees, and henceforth, after the drift period, we have as representative of the carboniferous formations peat bogs of different ages: some very thick, overlaid by strata of humus or of sand or gravel; some more recent, covering the ruins of monuments of the human race, bridges, roadways, aqueducts, &c., or holding in their matter bones of extinct or nearly extinct races of animals, like those of the aurochs, with utensils, weapons, and ornaments, attesting the existence of races of men now unknown. But some deposits of peat are so recent that their beginning is positively remembered by old men, who have seen them grow to some thickness where as children they had seen only stagnant pools, or a forest, or a muddy swamp. All these peat deposits, like the beds of coal and of lignite, are found in connection with vegetable remains which are either dead and cover them entombed in the clay of their surface, or are still living and deposit and heap their woody matter upon them, thus constantly increasing their thickness. We must therefore acknowledge that from the beginning of what we call the geological formations, or from the base of the Silurian to our time, remains of plants are found in intimate connection with all the deposits classed under the denomination of combustible minerals: marine plants or seaweeds, with the strata containing oil or bitumen; land plants, with the deposits of coal in all its degrees of hardness and perfection, from the soft peat, which is merely unripe coal, to the hardest anthracite.—The origin of the coal, or at least its essential composition, is apparent from what has been said of its geological distribution. The first hypothesis thrown out on the subject was that the coal was a mere mineral or bituminous compound deposited and distributed in the series of the rocks like strata of other nature. As it is mostly in concordant stratification with them, it was therefore considered to have the same origin. But the formation of the strata of the earth is easily accounted for: the sandstone by erosion of primitive rocks, the removal, transportation, and deposition of the matter; the limestone by the submarine action of animal life, &c. As free bitumen does not exist in nature, deposits of bitumen in the rocks are an anomaly as long as the origin of bitumen cannot be positively indicated. Moreover, there is a great difference between bitumen, or rocks impregnated with bitumen, and coal beds. Hardened or oxidated bitumen has been found in a few instances filling crevices of rocks, as in Canada and in West Virginia; the matter is homogeneous, either semi-pellucid, like dark-colored glass (the albertite), or a dull black compound comparable by its appearance to cannel coal (the grahamite), but filling holes, without concordance of stratification with the rocks wherein it is deposited, and proved by chemical analysis to be mineral oil oxidated and thus solidified by long exposure to atmospheric influence. Cases of this kind explain nothing concerning the origin and nature of coal, and therefore the first hypothesis was soon set aside.—That coal is composed of woody matter or of vegetable remains is easily recognized by ocular examination. In carefully inspecting a piece of coal the observer will in most cases see it formed of thin parallel layers of semi-transparent or crystalline matter, alternating with more opaque, earthy ones of the same thickness. These layers, about the tenth of an inch thick, are distinct enough to be counted like the rings indicating annual growth upon the horizontal section of a tree; and this even upon anthracite as well as bituminous coal. In splitting a piece of coal in the plane of stratification or of the layers, the exposed surface generally bears a pulverulent matter resembling charcoal; and this under the microscope is seen to be composed merely of vegetable fibres. Often the original form of the plants from which these woody fibres are derived (bark of lepidodendron, sigillaria, calamites, leaves and stems of ferns, &c.) is visible to the naked eye. In some cases a piece of coal a few inches square is seen with its faces covered with branches and leaves of ferns perfectly distinct in their outline and nervation; and in that way as many as five species have been identified upon the same surface, from their carbonized skeletons. In other cases, as in cannel coal, the fibrous texture of the matter cannot be recognized at first; but if thin layers of such coal are exposed to the action of a strong acid, the black bituminous substance is dissolved and the fibres are exposed whitened and distinct. Interesting researches have thus positively established the fact that coal is composed of vegetable debris. This conclusion agrees with the facts recorded above in regard to the distribution of the coal strata, which in the geological formations of all the epochs have been seen always in connection with vegetable remains.—But the essential fact, the origin of coal from vegetables, being admitted, the mode of nature's proceeding is not yet explained; and the question is still, whence have been derived the woody materials for the composition of the coal, and how have they been brought together and heaped in such immense masses of combustible as are represented by coal beds 10 to 20 ft. thick or more, extending over areas of many thousand square miles? Only two hypotheses are worth considering: that of the transportation and heaping of woody materials by water, and that of the growth of the materials upon the same surface now occupied by the coal beds. The first theory presupposes that forests growing upon slopes along lakes or seashores had been torn down by whirlwinds, and that the trees had been then carried by floods to the bottom of the lakes or to the sea, and there entombed and transformed into coal. This hypothesis could scarcely account for the formation of coal beds of very small extent. In the transportation of trees or vegetable remains by water, a large proportion of sand, mud, &c., would of course have been swept down with the forests, and mixed in the deposits with the wood, rendering the matter very impure. Moreover, the coal deposits are generally in flat basins of wide extent, and an equal distribution of the trees in horizontal layers is an impossibility by transportation of this kind. Another difficulty in the amount of woody matter which enters into the composition of a coal bed is not generally known, and is far above every hypothetical calculation. Considering areas of the same extent, a coal bed 6 ft. thick is equivalent to all the wood which could be produced by a forest in 2,400 years, and this supposing that, as is done in the government forests in France, all the wood should be cut in its prime and the cultivation of the forests cared for in order to force the productiveness to its highest degree. Some beds of the carboniferous measures of North America, the Pittsburgh coal, and the big vein, with an average thickness of 6 ft. at least, cover an area of more than 20,000 sq. m. Who would dare to suppose the production of such a mass of vegetation along a river, its carriage to the sea for 2,400 years, and its deposition upon a continuous surface in horizontal strata of an even thickness? Moreover, the lamination of the coal, its horizontal and continuous extent over wide areas, the formation of the shale above the coal (shale generally mixed with an abundance of vegetable remains, some of them very large), the presence of standing trees or standing petrified forests either in the clay beds under the coal, or even imbedded in the coal beds, or rooting in the clay beds above—all these facts, seen in connection with the coal formation and a number of others, are inexplicable by the theory of transportation. We have therefore to come to the second hypothesis, and to see whether coal beds proceed, like the peat beds of our time, from the growth of vegetables the debris of which have been yearly and successively heaped in place and then transformed into coal. This is called the peat-bog theory.—The formation of peat is generally little known or understood. Few works have been published on the subject, and as the bogs are generally of difficult and even of dangerous access, they are rarely examined carefully enough to obtain full evidence as to the details of their formation. And furthermore, this study demands a knowledge of botany and chemistry rarely attainable by the student before the years of his strength for field explorations are passed. Peat is formed in shallow water or in bogs, by the growth of plants which may be called bog plants, and which belong to a peculiar group of vegetables composed essentially of woody tissue and living either in water or above water, according to local circumstances. The species of plants forming peat in our time do not thrive out of the bogs, neither do land plants invade the bogs and contribute by their remains to the composition of peat. The bog plants demand first, for their establishment and their growth, a shallow basin of water with an invariable level. A basin of this kind is generally prepared in advance by the deposition of a clay bottom, produced from the decomposition of water plants or plants living entirely under water, whose tissue from this cause is not woody or fibrous; for the woody tissue of the plants is derived from the atmosphere, chiefly by the respiration of the leaves, and constitutes a part of the compound generally proportionate to the degree of humidity and the amount of carbonic acid of the atmosphere wherein they live. The conferves and the charas which fix lime or silex in their tissue and feed fresh-water mollusks, sometimes in immense number, are especially the plants which by decomposition form a kind of clay. In some circumstances this vegetation has, by its remains and those of the shells, established a thickness of muddy clay of 2 to 6 in. in a year. When this bed of clay has rendered the basin water-tight, it becomes a prepared ground for the growth of other plants, which, rooting in the soft bottom, ascend upon long stems or long stalks to the surface, where they expand their leaves and open their flowers. These are at the same time aerial and water plants; their tissue is woody like that of some species of mosses, which appear at the same time, and floating at the surface absorb carbonic acid and water by their innumerable small leaves, and thus have in their compounds as large a proportion of woody matter as the hardest wood. Every year the remains of this vegetation are pressed down to the bottom, and successively heaped till they reach the surface of the water. Of course this first deposit becomes in time solid enough to receive other kinds of plants which root upon its surface: species of mosses, sedges, and trailing bushes; then larger shrubs, then trees, which, with the smaller species that continue to grow under them, increase each year by their debris the amount of material which, constantly heaped, constitutes what is improperly called the growth of the peat. This is the simplest and most ordinary proceeding in the formation of peat. The process of transformation of vegetable matter into peat is due to the presence of water, as is apparent from a consideration of the different modes of decomposition of vegetable matter as explained by chemistry. When wood is immersed in water and thus guarded against the action of the atmosphere or of the carbonic acid which causes its decay, it is preserved sound for a very long time. Roman constructions, even foundations of the lacustrine buildings of wood, have been dug out still solid and unimpaired by decay from lakes and swamps of Europe; but the wood has become entirely black. When the materials which enter into the composition of peat are growing in a deep basin of water, and their debris are heaped under water, the preservation of the matter against rapid decomposition is then the direct result of immersion. The growth of the peat in cases of this kind may be stopped at the water level, where by a more complete decomposition of the plants a coat of humus is formed, which being invaded by land plants is transformed into a prairie or a forest.—But more generally peat grows above the water level, and then the production of the matter and its protection against the influence of the atmosphere are essentially due to the agency of a peculiar kind of moss, the sphagnum. This moss, which in deep water vegetates in loose extensive mattings, extending over the surface like a vegetable carpet, becomes out of water transformed into compact tufts, and its long slender stems, then growing closely pressed against one another, are knit together. The sphagnum is in that state a veritable sponge, endowed with an extraordinary power of absorption. Not only does it draw the water from below by its long capillary stems, which, growing without interruption, are imbedded very deeply in the matter of the bog, but it especially imbibes it from atmospheric humidity by its innumerable small leaves, and thus is constantly saturated with water. Its growth is rapid; where more space is afforded, it extends its plants all around, covering the whole surface of the bogs and every kind of woody debris spread upon it. Its tufts go up the roots of the trees, and surround the standing trunks one to two feet high; they pass over the prostrate trees and their branches, and bury them under a thick carpet which preserves them against atmospheric influence. In foggy countries, as in Ireland and Germany, the sphagnum ascends steep slopes and builds its peat deposits from the plains to the tops of high mountains. This moss is indeed by itself a remarkable phenomenon in the economy of nature; being a kind of balancing power, absorbing the useless surplus of water from the ground, from the swamps, and from the atmosphere especially, using it in part for its growth, carefully husbanding it for the preservation and transformation of all the woody tissue, its own included, into peat, and in dry seasons distributing the remainder to feed the numerous springs which have their source in the bogs. Thus, the peat bogs, like the glaciers of some countries, feed mighty rivers. In the Mississippi, for example, the blackness of the water, which is preserved as far down as St. Louis, proves its origin. It is nothing but bog water; hence its extreme salubrity and its remarkable incorruptibility.—Along the low shores of some lakes and of the sea, the bog vegetation sometimes begins from a sandy bottom without an intermediate clay bed. This happens especially when shallow basins of water are closed by sand deposits, and thus totally separated and guarded against the invasion of outside water and the muddy materials which might be brought upon it. These basins have a permanent level, and thus the work may proceed without interruption. The peat formed in that way rests immediately upon a bottom of sand, as coal beds are found sometimes also upon sandstone. It happens, however, that in some deeper part of the same basins the subaquatic vegetation is established, and its decomposition forms beds of clay or a clay bottom whereupon the old coal plants take root at a later period. The same bed may therefore at different places rest upon clay or upon sand. This fact also is remarked in coal beds of some extent whose bottom is at intervals either clay or sandstone. It also frequently happens, especially in small lakes and bayous, that the peat vegetation begins at the surface with floating masses, which gradually invade the whole space, covering it with a vegetable carpet. By successive annual growth and deposits this groundwork becomes thick and more solid; shrubs and even trees take root and grow upon it, till the mass becomes too heavy, is split or torn asunder, and sinks to the bottom. Other series of vegetation may begin again in the same way and be successively heaped upon one another, peat beds and forests, till the basins are filled. From some of these filled lakes now discovered under thick strata of humus, peat and wood, and even large trees which could be used for building, have been dug out to a thickness or a depth of 75 ft. or more. In New Jersey a considerable business has been done in fishing out of peat bogs the buried cedar timber. At other localities, as in the old bayous at the mouth of the Mississippi, floating islands, strong enough to support the construction of railways, have been formed in the same manner. Their nature is recognized by the vacillation and unsteadiness of the ground, which undulates under the pressure of a heavy weight like that of a railway train. At other places, as in the Dismal swamp, the formation is mixed. A bed of peat 15 ft. thick is formed over the swamps around Drummond lake, by the debris of large trees and of an impenetrable grove of canes, whose roots penetrate deeply into thick layers of sphagnum. It is there extremely difficult to reach the borders of the lake. They are mere floating moors, sinking under the weight and formerly extending over and covering the whole surface of the lake. This is proved by a layer of trees strewn at the bottom of the lake, and the process of nature may be seen still in activity along the borders, where large trees (bald cypress), sunk into the water, perhaps 8 ft. deep, are there slowly decaying in a standing position. Their trunks are already generally hollow, only the bark and a thin crust of wood being left; the water enters them of course, and fills them with the debris floating upon the surface, especially cones and leaves. In time these decayed trunks fall to the bottom and are there imbedded either for slow decomposition to peat, or if covered with mud petrified by the softening of their tissue and the impregnation of mineral matters. In that way the hollow trunks discovered in the coal beds of England and Canada have been petrified; their bark only is preserved, and they are filled with cones, leaves, insects, shells, &c. These fossil trees were looked upon for a long time as an inexplicable wonder.—Various circumstances, as local depressions which bear water upon the surface of the emerged peat bogs and destroy their vegetation, stop the growth of the peat and change the surface into mud swamps. This is especially caused by alternation of level, or by the ground being covered with water at one time of the year and dry at another. Then the decomposition of the plants is rapid and entire, and its result is a kind of mud increased by the introduction of foreign materials brought by water. Leaves and vegetable debris are often imbedded in this matter and thus preserved by petrifaction. This represents the formation of the laminated clay shale which generally covers the coal beds as a roof, and contains in some localities vegetable remains in a beautiful state of preservation. Of course, these changes of level were formerly, especially at the carboniferous period, more frequent than now; for then the land was mostly of insecure formation, half floating, and along the sea immense tracts of land were engulfed, and so deeply sunk that their surface was covered with sand by the currents, or even at a greater depth invaded by the animals building and forming limestone deposits, shells, madrepores, corals, &c. In this way the formation of the sandstone and limestone which in some places overlie the coal beds without intermediate shale is easily understood. Cases of a similar nature are recorded from the peat bogs of our time. It has been said already that in Holland old peat bogs have been discovered by borings, at a depth of from 60 to 100 ft. below the surface, placed upon one another and separated by clay deposits of 30 ft. or more. The great peat bogs between the lakes along the foot of the Jura mountains in Switzerland sink in places under the sands of the lakes and are covered by gravel. At other localities the peat deposits of a thickness of 10 ft. are cut in the middle by a layer of coarse sand varying from 6 to 12 in. in thickness. We see therefore in the present formation of the peat bogs a counterpart of that of the coal, represented in all its details, though in a reduced proportion. Not a single case has been recorded in regard to the formation of coal which cannot find its counterpart and its explanation in some of the phenomena attending the present formation of peat. In the countries where peat banks are exposed and worked to their base by drainage, and where the nature and distribution of their materials can be studied upon the exposed face of the beds, these compounds are seen constantly and extremely variable: heaped remains of woods, of mosses, sometimes whole forests prostrated and imbedded. But in these beds the alternation of the annual layers is always easily recognized. Near the top their thickness is generally more than an inch; near the base they become by maceration and compression reduced to one sixth of an inch or less. In the oldest peat bogs, the lower layers are formed of a soft pellucid matter resembling a black glue, alternating with a more opaque and fibrous material, thus exactly corresponding in their appearance to the pellucid and opaque laminæ of the coal. Hardness or induration of this old peat seems to the eye the only process needed to transform it into coal. The submerged peat, that of the lakes or of the seashores, frequently and extensively formed in Holland, North Germany, and elsewhere, is not laminated; the matter is generally compact, homogeneous in aspect, and nearly reduced to paste, at least in its more advanced stage of decomposition. The difference is caused, as remarked already, by the semi-aquatic nature of the plants which enter into its composition, and which, being less fibrous than those growing upon emerged bogs, are more easily and equally transformed under water. This process explains the difference between the laminated bituminous coal and the compact homogeneous cannel. The immense trunks mixed in the beds of laminated coal evidently prove that some of the beds were formed above water. On the contrary, cannel coal, whose compounds, so far as they can be recognized as vegetable remains, are essentially the floating trunks and branches of stigmaria, indicates as evidently that in this case the coal was formed of plants floating or submerged, thus presenting the two essential differences which are recognized in the peat beds of our time. Local variations in the phenomena attending the formation of immersed peat are quite as frequent and remarkable as in the formation of the emerged peat bogs. It would require a volume to describe them in detail. Near Kiöogge in Denmark, along the seashore, extensive peat deposits now covered by a layer of humus forming prairies are composed merely of birch trees, whose bark is separated from the decomposed woody matter; this is a semi-fluid brown paste at the bottom, 4 to 6 ft. thick, and the bark at the surface forms a layer of hollow cylinders or compressed sheets without any woody matter between them. The exploitation of these deposits is made to get the woody paste, which is taken in buckets from under the layer of bark, spread upon beds of straw, and when somewhat hardened by the percolation of water is kneaded, flattened, and pressed with shovels, and then cut and dried, thus forming a very valuable fuel. The bark is left out of the trenches as of little value. We have in this case the illustration of a peculiar formation of some beds of coal whose top is overlaid by a stratum mostly composed of pieces of bark of lepidodendron, sigillaria, calamites, &c., pressed upon one another without even laminæ of coal between the layers. At Trevorton in Pennsylvania, a bed of semi-anthracite thrown up to the perpendicular is roofed by such a layer of petrified bark, and exposed like a wall of mosaic work, diversified by the impressions which mark the surface of the bark of most of the species of trees of the carboniferous period.—It has been objected to this theory of the production of coal, that the peat beds, however thick they may be, could not account for the immense mass of combustible minerals or of woody matter contained in a coal bed even of moderate thickness. This is a great mistake, for indeed nothing but the growth of the materials upon the place where they have been buried and transformed into coal can satisfactorily account for the immense proportion of woody matter in the deposits. The comparative caloric power of wood, peat, and coal has been found to be on an average represented by the proportion of 30 for wood, 37 to 40 for peat, according to its age, and 60 for bituminous coal. We have seen above what is the average production of wood under the best regulated cultivation of Europe. The growth of peat, as recognized from repeated observations, also made in Europe, averages one inch a year at the surface. By compression and decomposition the matter is reduced toward the base of the banks to one sixth or even one eighth of the original thickness. Comparing this production with that of the wood of a forest upon an equal area and in the same period of time, we see from the same records quoted above that the peat yields in cubic feet, after desiccation, twice as much combustible matter as the forest. Peat bogs are now, especially in wet countries, as in Ireland, Sweden, and Russia, not only of wide extent but of great thickness. In Switzerland and Germany the average thickness of peat beds is 8 to 12 ft.; but in the same countries the peat attains in some localities a thickness of 30 ft. in continuous and extensive beds. In Ireland, Denmark, and other northern countries, there are beds of combustibles formed of peat alternating with prostrated forests, from 60 to 80 ft. thick or more. Now, a bed of peat 30 ft. thick, comparing its matter with coal according to the proportion of 40 to 60 for caloric produced, and deducting one half for drying the matter and rendering it fit for fuel, would represent an amount of woody matter equal to that of a bed of coal 10 ft. thick. It is therefore conceivable that at the carboniferous period, when the atmosphere was saturated with vapors and carbonic acid gas, the essential elements which feed the plants and supply woody tissue, the luxuriance of the vegetation must have been far above that of our time. The heaping of the vegetable remains must then have attained in favorable localities a thickness at least double that of the present peat deposits. The supposition that the plants at the carboniferous epoch contained more bitumen than those of our time has no foundation whatever, as bitumen is obtained from peat in as large proportion as from coal. Mineral oil, which also results, in its essential part at least, from the decomposition of vegetable matter, is in this particular only comparable to coal; but it is produced from marine plants which have no fibrous tissue, but merely cellular matter.—After reading the foregoing descriptions of the growth of peat, the admirable simplicity of the process used by nature to reach its end in providing deposits of combustible minerals in the several geological periods is evident enough. This identity, however, can be still more positively proved by comparing the chemical operations attending these formations, and the absolute similarity of the elements which compose the different matters known under the names of peat, lignite, coal, and anthracite. The composition of these combustible materials, as they are generally called, compared with that of wood and of woody plants which by their characters and texture are related to the most common species of the coal measures, and which enter into the composition of peat in our time, is presented in the following table compiled from Dana's “Manual:”

SUBSTANCES.  Carbon.   Hydrogen.   Oxygen. 

Wood 49.66 6.21 43.03
Lycopodium dendroideum  48.70 6.61 43.25
Lycopodium complanatum  48.43 6.61 43.02
Equisetum hyemale 47.50 6.68 44.49
Sphagnum 49.88 6.54 42.42
Peat 59.5  5.5  33.0 
Brown coal or lignite 68.7  5.5  25.0 
Bituminous coal 81.2  5.5  12.5 
Anthracite 95.0  2.5   2.5 

This table shows in lycopodium species and equisetum about the same composition as in wood. These correspond in structure, and have at the same time a generic relation to the species forming the essential compounds of coal as recognized by microscopical examination, viz.: lepidodendron, sigillaria, and calamites. The sphagnum, which enters more than any other plant into the composition of peat, has more carbon than lycopods, even slightly more than wood. In the decomposition of the woody matter two different processes are recognized by chemistry. Decayed wood taken from the interior of trunks of dead trees exposed to atmospheric action gives by analysis, on the average, carbon 47.62, hydrogen 6.18, oxygen 44.87; which compared with wood, C. 49.66, H. 6.21, O. 43.03, indicates that through this decomposition a proportion of carbon has been taken from the wood, while the hydrogen is slightly increased. The elements of water therefore, and an amount of oxygen, have become united with the wood, while carbonic acid has been separated from it. This comparison of analyses exemplifies the well known fact that the decomposition of plants under atmospheric influences returns to the atmosphere the carbonic acid absorbed by the vegetation, which by nutrition of the living plants is transformed into wood. But when the woody matter is protected against the action of the oxygen of the air, as it is in vegetable remains under water or covered by mosses impregnated with water, the chemical changes as proved by analyses assume another form. This is the case in the formation of peat, which when ripe has C. 59.5, H. 55, O. 33, or compared with wood an increased amount of carbon in proportion with a diminution of oxygen, separated into carbonic acid with a little of the hydrogen of the wood. The amount of carbon in peat, as in all the mineral combustibles, is extremely variable; in young sphagnum peat it is no more than 51 to 52 per cent., while in old peat it is as high as 61 to 62 per cent. The proportion of bitumen increases in peat in the same degree. Taken from old beds, this matter has yielded by distillation 30 per cent. of bitumen. To obtain it, the distillation of peat has been practised for many years on the bogs of the Jura in Switzerland; and peat from the bogs of Ireland is also distilled in large establishments for manufacturing candles. This sufficiently answers the objection made against the theory of the formation of coal from heaped vegetables by annual growth like beds of peat, and the mistaken assertion that peat has no bitumen and therefore cannot form coal. The composition of peat as given above does not differ much from that of the more recent lignite of Germany, showing therefore the same process of chemical action. These lignite beds, mentioned before, are heaps of trunks overlaid by thick strata of sand and clay. The wood is black and quite soft, but its texture is still as well preserved and as distinct as in living trees. The matter in its purity has C. 57.28, H. 6.03, O. 36.10, or a less amount of carbon than old peat, with more oxygen; thus proving that the process of decomposition is exactly the same, but that it is in a less advanced stage. In lignite of an older formation the analysis indicates C. 68.7, H. 5.5, O. 25; therefore an increase of carbon, still resulting from the same combination, the diminution of the oxygen and of a little of the hydrogen of wood. As in peat, the amount of carbon in lignite is very variable, which results especially from the nature of the original compounds. The lignite of the old tertiary of the Rocky mountains, which in many beds has the same appearance, lamination, and nearly the density of the true coal, has only 51 per cent. of carbon in an average taken from the comparison of 21 analyses of the matter from many localities. This reduced amount of carbon is apparently due to the great proportion of palm wood and palm remains which entered originally into its composition. The average composition of the best qualities of bituminous coal is C. 81.2, H. 5.5, O. 12.05; showing still the same proportion in the diminution of the oxygen and the increase of carbon. The chemical action is therefore constantly the same, and is recognized in the whole process; that is, the slow combustion of the woody matter by the action of the oxygen which it contains, or contained originally. Chemistry has not perfectly explained the process, or obtained similar results and products by its experiments. Prof. Dana says that the changes attending the ultimate decomposition of woody matter into coal depend: 1, on the affinity of the carbon for oxygen, making carbonic acid; 2, on that of hydrogen for oxygen, producing water; 3, on that of carbon for hydrogen, making carbo-hydrogen gas or oil; and 4, on the tendency of the carbon and the hydrogen under certain proportions to form with a portion of oxygen the staple compounds included in the term coal. In anthracite the amount of carbon is still increased, while that of hydrogen and oxygen has become proportionally less, and the volatile matter is reduced to a minimum. Hence pure anthracite is debituminized and burns without any flame. The anthracite of Pennsylvania becomes harder and more free from gas in proportion to the distance of the basins eastward from the Allegheny mountains, where its beds are folded in more numerous and sharper flexures. It has been supposed that its debituminization had taken place from some cause connected with the uplifting of the mountains. The first supposition was that the coal had been reduced to anthracite by heat. This opinion has been contradicted by another hypothesis which ascribes the transformation to great compression of the mineral coal by the upheaval of the mountains between whose sides the basins were slowly pressed, and thus slowly forced into numerous folds, and perhaps to a considerable amount of caloric produced by mechanical agency, movement, compression, &c. Many facts seem to contradict this last hypothesis, and support the opinion that the original heat of the earth has contributed to the metamorphism of the coal, as it has to that of the rocks. The problem is however complex, and cannot be discussed in a few words. The facts have to be recorded, and the conclusions may become evident in time. In Pennsylvania the debituminization decreases in proportion to the distance eastward from the mountains. At Trevorton, in Zerbe's gap, the coal is semi-anthracite; it has 84 to 86 per cent. of carbon, 7.50 of inflammable gas, and 2.50 of water. Though this basin is far distant from the mountains, the undulations of its beds are nearly as sharp as those near Pottsville and Tamaqua, being inclined at an angle of 50° to 60°. As the thickness of the strata is great, the pressure seems to have been equal to that nearer the mountains. In the Rhode Island basin the anthracite is still harder and more debituminized. Here the undulations are repeated, very numerous, and short, but not sharp, resembling the waves of the sea, and the strata are not thick; but the anthracite is in close proximity to the primitive rocks, and the shales over and under the coal show by their color and density the evident traces of metamorphism. There is here a peculiar phenomenon marking the influence of heat; it is the liquefaction of the shale and the effects of it on the vegetable remains, particularly the ferns. Their branches are generally elongated in one direction and contracted in the other side, as though drawn to one direction by the flexure of the shales in a state of semi-fusion. The plants too bear upon their surface a kind of intumescence, seemingly produced by heat. At Trevorton the shales over the coal are more or less marked by small round holes varied in size, filled with a pulverulent bituminous matter which looks as if formed by a kind of ebullition, or rather by gas forcing its way from the anthracite and stopped and enclosed within the shale. In Arkansas the Spadra coal is semi-anthracite. The strata wherein it is interlaid are nearly horizontal, their dip scarcely marked by an angle of 2°. It is also at a distance of 30 m. from the mountains. It has about the same composition as the Trevorton coal, 88.75 per cent. of carbon, with 7.7 of volatile matter. The rocks all around in the country bear traces of metamorphism, and the change by heat becomes more and more evident in advancing toward the Hot Springs, a volcanic region, away from the mountains. The same phenomenon is still more evident, and its cause more appreciable, in the tertiary lignite basins of the Rocky mountains. At Golden, Colorado, the thick lignite beds, 12 to 16 ft., are thrown up to the perpendicular by compression, in close proximity to the base of the uplifted granitic mountains, and between them and thick deposits of lava. This coal is soft, bears no trace of metamorphism, and even crumbles from the contact of the atmosphere. In New Mexico the strata are horizontal, but split by thin dikes of basalt, along which the coal shale is changed by heat and nearly as hard as silex. The nature of the coal in contact with these dikes has been recorded from a locality further south, near the valley of the Gallisteo, where the Placiere coal at one exposure of the bank is true lignite, while at another exposure, and in contact with an enormous dike of basalt, it has been changed into true anthracite, having 89 per cent. of carbon and only 3.18 of volatile matter, while at a distance from the dike the amount of carbon is only 58 per cent. The dip of the strata even in coming closely in contact with the dikes varies between 10° and 14° only. These facts are evident proofs of the debituminization of the coal and its change to anthracite by the action of heat. In this we have at the same time an insight into the chemical changes causing the modification of vegetable matter and its transformation into coal. For the action of heat does not deprive the coal of any part of its constituents; it merely quickens the slow burning or metamorphosis of the matter, the ultimate result of which is the entire reduction of the oxygen- and hydrogen-producing volatile gas into compact or condensed mineral combustible, a mere compound of the original elements of wood modified under peculiar influences.—The great Alleghany coal field extends from the middle of Alabama to northern Pennsylvania, and occupies portions of Alabama, Georgia, Tennessee, Kentucky, West Virginia, Virginia, Ohio, and Pennsylvania. It contains from 50,000 to 55,000 sq. in. of coal area, and all the coal beds and groups of beds described under the title Anthracite, the nomenclature of which will be adopted herein. In some portions of the anthracite fields the millstone grit or conglomerate is interstratified from the bottom to the top of the coal measures, though much more massive near the bottom than in any other portion. It is also much thicker in the eastern part of these fields than in the western portion, and likewise more massive than in the bituminous fields, or westward generally, as the foregoing table indicates. A group of coal beds, O, not shown in the anthracite column, though existing there as “nests” of imperfect coal below A, are found AmCyc Coal - Alpha group.jpg
A, or Alpha
at irregular intervals throughout the Alleghany coal field; but these beds are thin, impure, often absent, and rarely of workable size or merchantable quality. They exist both below and in the millstone grit when found, and are more persistent and regular in the western than in the eastern coal fields. The first group of regular beds is A; these also exist in the conglomerate in the Pennsylvania anthracite fields, and in some of the outlying basins of the Alleghany field; but generally they consist of two small, unworkable streaks of impure coal, or a single bed of earthy coal 1 to 4 ft. in thickness, resting on or near the millstone grit. It produces the block or AmCyc Coal - Buck Mountain group.jpg
B, or Buck Mountain.
furnace coal of Pennsylvania. The next group, B, consists of two regular and excellent beds, which are generally united as a single bed, though always divided by a streak of slate or fire clay, which often expands to 20 ft. or more. This bed, or group of beds, is the most regular of all the American coal beds; and, being the first large, workable, and productive bed, its horizon is the most extensive, and nearly equal to the area of the entire field, while it can readily be identified in the central if not the western coal field. These beds, when united, are from 4 to 7 ft. thick, and singly from 2 to 4 ft. each. Immediately above this group, sometimes resting on the coal, but generally separated by slates and shales, is the micaceous sandstone, or “buckwheat rock” of the Pennsylvania mines, which is a coarse, massive sandstone, filled with mica scales. This rock is very persistent, and can be identified in all the great American coal fields of the carboniferous age. This great bed of sandstone, which is often 20 to 60 ft. in thickness, is followed by shales and the fossiliferous or ferriferous limestone, and the AmCyc Coal - Gamma group.jpg
C, or Gamma.
buhrstone iron ore, which are generally present in the Alleghany coal measures. The ore ranges from 10 to 20 in., and the limestone from 10 to 20 ft. in thickness. This is succeeded by shales and the group of coal beds.C. In the anthracite regions, and generally in the bituminous fields, this group consists of two thin, slaty, and AmCyc Coal - Skidmore group.jpg
D, or Skidmore.
unworkable beds; but one of them frequently expands to 3 and even 5 ft. of excellent splint or cannel coal. It is the celebrated Peytona cannel bed of Coal river, West Virginia, and the Grayson cannel of Kentucky. This group is succeeded by shales and sandstones of variable thickness, from 50 to 150 ft., on which rests the bed D, which is always single, and generally pure and workable, from 30 in. to 4 ft. in thickness. Above this bed, separated by AmCyc Coal - Mammoth group.jpg
E, or Mammoth.
sandstones and shales, is the Curlew or Freeport limestone, 8 ft. thick; and on or near this rests the group E, which embraces two or three beds of coal, each generally from 2 to 4 ft. thick, which often unite as a single bed of 6 to 12 ft., divided by slates. This group forms the celebrated mammoth bed in the Pennsylvania anthracite fields, and the Freeport beds in the western part of Pennsylvania. Above this group (which is very confusing to the miner and the geologist, on account of its irregularity and uncertainty in uniting and dividing) from 20 to 50 ft. of soft black shales or slate are generally found, and on these rests the Mahoning or mammoth sandstone, which is the largest regular sand rock in the Alleghany coal measures, ranging from 50 to 75 ft. in thickness, divided by one and sometimes two thin coal seams, and several feet of slates or shales. Streaks of quartz crystals are often found between the upper and lower strata of this great rock, which is a quartzite, and often a conglomerate rock, 80 ft. thick in the anthracite measures. It is sometimes accompanied by a stratum of white quartz secretions, AmCyc Coal - Holmes group.jpg
F, or Holmes
or conglomerate, even in the western portions of the field, which are often mistaken for water-worn pebbles. This is a great landmark in the Appalachian coal fields, which cannot well be mistaken, and yet it is often misplaced. Above this exists the group F, which consists of two thin impure beds, divided by a few inches of fire clay, known as the rough bed in the anthracite fields, where it is 5 to 7 ft. thick, and as a single bed in the Allegheny field, 1 to 2 ft. thick of slaty and sometimes 3 ft. of cannel coal. It seems to be a true horizon of coal, but is seldom found in merchantable quantity or quality. Above these are from 200 to 300 ft. of shales, slates, sandstones, and limestones, followed by the bed G, which is the large and celebrated Pittsburgh bed, remarkable for its production of excellent gas, coking, steam, and household coal, combining all the qualities of every variety of bituminous coal except the block and cannel. It ranges from 6 to 12 ft. in thickness, averaging from AmCyc Coal - Primrose group.jpg
G, or Primrose.
6 to 8. Between these great beds, E and G, exist from 300 to 450 ft. of unproductive strata, which contain no workable beds of coal. These are known in Pennsylvanian nomenclature as the lower barren measures, which are as distinctly marked in the anthracite as in the bituminous fields of this state. It may be briefly stated that all the coal beds and coal measures existing in the anthracite fields above G are found in some portions of the Alleghany field; but the coal beds are thin, rarely workable, and cannot be identified. From 1,000 to 2,000 ft. of coal measures are supposed to exist above G; but these are known as the upper barren measures, and are made up chiefly of shales, with a few coarse sandstones and massive limestones, one of which is 70 ft. in thickness, and is distinctly defined over a large area. The general average thickness of the coal measures between B and G is 1,000 ft., but varies from 500 to 1,200 ft. From the carboniferous limestone to B, including the groups O and A, the thickness of the strata is from 200 to 500 ft., and the total thickness of the coal measures about 3,000 ft. in Pennsylvania, with a minimum thickness of 30 ft. and a maximum of 50 ft. of coal.—The distribution of the deposits of coal in North America, is well adapted for the supply of the wants of the present inhabitants. The largest population is along the Atlantic coast, and the best coal, that of the anthracite fields of Pennsylvania, happens to be situated nearer the largest markets than any other, being less than 200 m. from New York and less than 100 m. from Philadelphia. The basins producing it are small, containing in all but 470 sq. m.; but the beds are very large and numerous, and the quantity produced is about half of all the coal mined in the United States. (See Anthracite, Lackawanna, and Wyoming Valley.) In the eastern central part of Pennsylvania, where the anthracite basins are situated, great disturbances of the strata have taken place after they were deposited, caused by the gradual upheaval or subsidence of alternate portions in N. E. and S. W. lines, so as to throw them into a waving form. This disturbance was greatest toward the S. E., and the rock arches become wider and flatter as we go N. W.; but they extend S. W. entirely across this state and Maryland, and their effects are even seen in the coal field of eastern Ohio. All anthracite coal is found in regions where the strata have been considerably disturbed, or where from local causes it has been subjected to heat. Next westward from the anthracite in Pennsylvania the coal is semi-bituminous, and still further west it is of the ordinary bituminous character, the quantity of volatile matter constantly increasing toward the central part of the field. The carboniferous formation terminates in the northern part of Pennsylvania, and the division into counties of that district happens to correspond with six of the great flexures of the strata before mentioned, which give rise to six coal basins. Some of these from their far northern position contain some of the richest and most productive mines in the state. They produce, for the supply of the coalless country north of them, the variety commonly called Blossburg, which is used for steam and manufacturing purposes. The deposits of coal extend in this northern district along the middle or bottom of the basins only, in lines of small detached fields or chains of basins, which are more extensive as they are followed S. W. until they become uninterrupted prongs or finger points. Still further S. W. in Pennsylvania the lower beds arch over portions of the intermediate anticlinals, and in the S. W. part of the state, in the Pittsburgh country, the four or five lower beds which alone occur further N. disappear on the surface, dipping under a red and gray shale formation in which are no coal seams. Above these barren measures in the highest ground about Pittsburgh appears another bed of excellent coal, named after that city, from which all the coal is mined that is used in the S. W. part of the state, large quantities of it being also sent down the Ohio and Mississippi rivers. Pennsylvania not only supplies the United States with all the popular fuel anthracite, but she also produces more bituminous coal than any other state, of which she has every variety of excellent qualities. The northern districts in 1873 produced 1,500,000 tons, and the eastern margin of the field 1,000,000 tons of semi-bituminous coal. Of the common bituminous coal 9,000,000 tons were mined in that year, chiefly in the Westmoreland and Pittsburgh districts and along the Monongahela and Youghiogheny rivers, for the supply of all the western states by way of the Ohio and Mississippi rivers, for gas making in the eastern cities, and for domestic and manufacturing purposes in the state. This is therefore the greatest of all the coal-producing states; and from its geographical position, its rich endowment of other minerals, and other natural advantages, there is every probability of its continuing to retain this position for a long time. The coal field which covers the eastern part of Ohio is the western border of that of western Pennsylvania. It stretches along the Ohio river from the Mahoning river on the north to near the Scioto on the south, from two to four counties in width, embracing 10,000 sq. m., being nearly as large as that of Pennsylvania, which has 12,774 sq. m. of coal. Along the N. E. border is found a peculiar splint or block coal, which has been used for many years in its raw state in blast furnaces; some small basins of it also occur on the Pennsylvania side of the line. Further south, in the Hocking valley, occurs a coal bed of extraordinary size, measuring in some localities 12 ft. in thickness, and it is said that it can also be used like the block coal.

AmCyc Coal - Appalachian Formations.jpg
Fig. 5.—Appalachian Formations, Ancient and Modern.

References: Modern.—a, the Atlantic sea; b, recent or cretaceous formations; c, granitic and volcanic; d, mesozoic, new red, &c.; e, metamorphic, gneissic, &c.; g, sandstones and limestones of the valley, or the lower palæozoic formations; h, slates and shales of the oil-producing formations; i, sandstones overlying the oil strata, including the old red and the conglomerate; j, the anthracite coal deposits; k, Cumberland coal field; l, l, n, Alleghany coal field; m, Ohio river.

The Potsdam sandstone underlies the Auroral limestone, g, and overlies the gneiss, e, which must exist to some extent in the entire basin. The dark vertical trap formations emerge from the granite, and were the means of forming the gneiss.

Ancient.—No. 1 corresponds to a, and is the granite seacoast line, forming the volcanic boundary of the ancient sea; 2 is a deep view of the volcanic vent between the granite and the gneiss, which is formed of the vented matter; 3 is the metamorphic or early gneissic sedimentary rocks; 4 corresponds to g, and is the base of the palæozoic; 5 is the bituminous slates of the oil strata, followed by the massive sandstones of the old red, and the subcarboniferous; 6 is the ancient sea, since filled by the sedimentary deposits represented in g, h, i, j, k, l, &c.; 7, 7 is the line of volcanic vents existing in the plutonic or granitic coast line, which extends from Maine to Cuba. The form of the ancient structure is of course ideal, and the two views are thus given together in order to convey an impression of the cause and its effects.

The production of coal has not been very large in Ohio (about 4,000,000 tons), but from the building of railroads, and the increase of population and manufacturing, the coal trade of the state is rapidly increasing. Maryland has a very small but very valuable basin of bituminous coal near the Baltimore and Ohio railroad, extending from near Cumberland to Piedmont in the western angle of the state. The production in 1873 was 2,674,110 tons, and since the opening of trade in 1842 the total production has been 24,027,786 tons. It is sold chiefly at New York for the use of ocean steamers and other steam purposes, is known as Cumberland coal, and is semi-bituminous; the bed is 14 ft. thick. West Virginia is almost wholly underlaid with bituminous coal, forming a portion of the same field above described in Pennsylvania, Ohio, and Maryland. The upper coal measures, including the Pittsburgh bed, extend over a large space in the N. W. part of the field in this state, along the Ohio river, as far south as the mouth of the Guyandotte. In the northern part of the state these upper coal beds are developed of good size and quality along the Baltimore and Ohio railroad and on the river about Wheeling. There are very fine natural exposures of the lower coal measures on the Kanawha river, from the great falls to Charleston. The display of coal in this district is very remarkable, and it has recently been made accessible by the completion of the Chesapeake and Ohio railroad. There are other very extensive districts in West Virginia, both N. and S. of the Kanawha, where there is known to be a great abundance of excellent coal in localities to which no railroads have been built. There is little or no doubt of the identity of the coal beds throughout the states of Pennsylvania, Ohio, Maryland, West Virginia, and eastern Kentucky, which shows a wonderful sameness in distribution throughout all this vast territory. This coal field extends over the eastern part of Kentucky, and in the northern part of it in this state the Ohio and West Virginia coal beds of the lower series are found, but in the southern counties of the field only the subconglomerate coal beds appear. Very little development has taken place in this district, except on the Ohio river. Tennessee has an interesting and valuable coal field, which is coextensive with the table land of the Cumberland mountain, forming the western boundary of the valley of East Tennessee. In the more northern part of it the lower coal measures of the states further north seem to be found, but the great body of the field is composed of the coal beds still lower in the series which are found in West Virginia and eastern Kentucky. The conditions for coal making appear to have existed in the south earlier than further north; consequently coal is found in rocks which in the north are subcarboniferous and produce no coal. Alabama has the southern extremity of the great coal field we have been describing, divided into three separate portions called the Black Warrior, the Catawba, and the Coosa fields, containing in all 5,330 sq. m. Some of the best deposits of iron ore in America are east of and in the immediate vicinity of the coal fields of Alabama, Tennessee, and West Virginia, which at some future time will make this the seat of large iron manufactures. Thus far, however, but little has been done to bring into use these vast treasures of fuel. This first, Alleghany, or great eastern coal field of the United States, containing in all 58,737 sq. m., is by far the best and in all respects the most important in America.—When the first geological researches were in progress in the western states, it was supposed that the coal beds and the series of coal-bearing rocks were the same in Illinois, Indiana, and western Kentucky as in Pennsylvania, but it is now proved that they are entirely different and never were connected. The recent geological survey of Ohio shows that the great anticlinal axis which passes from Lake Erie past Cincinnati and through the eastern parts of Kentucky and Tennessee is much older than the coal-making age, and that the coal fields of Michigan and Illinois were always separated by it from that of Ohio. The peninsula of Michigan contains a coal field of 6,700 sq. m., extending from Jackson to Saginaw bay, but the coal-bearing rocks are only about 100 ft. thick, and contain but one bed of coal of about 3 ft. or less of coal of a bad quality, full of sulphur and other impurities, and the annual production is small. The materials of its rocks were derived from the north. The third great coal field covers 6,500 sq. m. in the western part of Indiana, 36,800 sq. m. in Illinois, and 3,888 sq. m. in the western part of Kentucky. The best coal produced in this field is from Indiana, where along the eastern border of it there is a good quality of block coal for furnace use, and some common bituminous coal of fair quality. The Illinois coal is all much inferior to that of Pennsylvania and Ohio, contains a portion of hygrometric moisture which lessens its heating power, and considerable sulphur and other injurious impurities. Notwithstanding this, it is invaluable to the state, which is almost wholly a prairie country, mostly level, destitute of trees, covered in a state of nature with tall coarse grass, and with an extremely fertile soil. The want of fuel of any kind would have been a great disadvantage; and inferior as it is, considerable quantities are annually produced in many parts of the state, especially opposite St. Louis and near other large places. The portion of this field extending into western Kentucky is believed to contain better coal than that of Illinois, and it now produces moderate quantities from mines near the Ohio river.—The fourth great coal field lies west of the Mississippi river, in western Iowa, southeastern Nebraska, northern Missouri, eastern Kansas, the Indian territory, and western Arkansas, and possibly it underlies the cretaceous formation which on the surface separates it from the Texas coal at Fort Belknap; it contains in all nearly 80,000 sq. m. The deterioration westward of the coal continues over this field also, there being fewer and thinner coal beds and coal-bearing rocks, the latter becoming gradually converted into vast beds of limestone, and the shales and sandstones among which coal is usually found becoming subordinate. The best and most productive portion of this field is the district in Iowa along the Des Moines river. In S. W. Iowa and N. W. Missouri, in Nebraska, and the western border of the field in Kansas, the upper coal measures, a great limestone formation very similar to the subcarboniferous limestones below the coal, comes in, containing only one or two very thin beds of coal about one foot thick. The middle coal measures are but little better, the valuable coal beds all being found in the lower coal measures. On the Des Moines river are some beds of fair size, and there is a considerable production. In Missouri, where the lower coal measures are exposed in a district containing 12,420 sq. m., extending from the Iowa line in the N. E. part of the state S. W. across the Missouri river to the Kansas line near Fort Scott, there are workable beds from 2 to 3 ft. thick, and in the absence of better fuel there is local demand for a considerable quantity of the production. This productive coal belt extends into the S. E. corner of Kansas, whereas in the other parts of the state where the coal extends the seams near the surface are only about one foot thick. The dip of this coal field is toward the northwest, and on its western border Permian fossils are found, this being the only locality where that formation has been found on this continent.—According to the United States census, the statistics of coal production for the year ending June 1, 1870, are as follows: Number of collieries, 1,566; hands employed under ground, 65,000; above ground, 29,854; total, 94,754; capital employed, $110,008,029; wages paid, $44,316,491. Bituminous coal mined, 17,199,415 tons; value, $35,029,247. Anthracite coal mined, 15,664,275 tons; value, $38,495,745. Total coal mined, 32,863,690 tons; value, $73,524,992. The distribution of the production of coal in the United States in the chief coal-producing states is shown in the following statement from the census of 1870. Except in the case of Pennsylvania, the production is bituminous coal:

No. of
Value of

Alabama $26,000  11,000  $39,000
Illinois 322  4,288,575  2,624,163  6,097,432
Indiana 46  554,442  437,870  988,621
Iowa 96  618,332  263,487  874,334
Kansas 20  166,430  32,938  114,278
Kentucky 30  717,950  150,582  446,792
Maryland 22  23,891,600  1,819,824  2,409,208
Michigan 176,500  28,150  104,200
Missouri 56  2,587,250  621,930  2,011,820
Ohio 307  5,891,813  2,527,285  5,482,952
Pennsylvania 588   67,911,703   28,448,793   52,357,814
 Anthracite 227  50,922,285  15,650,275  39,422,775
 Bituminous 361  16,989,418  7,798,518  12,985,039
Tennessee 11  313,784  133,418  330,498
Utah 44,800  5,800  14,950
Virginia 779,200  61,803  221,114
West Virginia 41  1,434,800  608,878  1,035,862
Wyoming 250,000  50,000  800,000

The total production of coal in the United States in 1873 was as follows:

of coal.

Pennsylvania 12,774  34,523,560
Maryland 550  2,674,100
Virginia 185  60,000
West Virginia 16,000  1,000,000
Ohio 10,000  3,944,340
Eastern Kentucky 8,983  50,000
Western Kentucky 3,888  350,000
Tennessee 5,100  400,000
Alabama 5,330  60,000
Michigan 6,700  50,000
Indiana 6,450  1,500,000
Illinois 36,800  3,500,000
Iowa 18,000  350,000
Missouri 23,100  1,000,000
Kansas 17,000  50,000
Colorado, Wyoming, Utah, &c.—lignite  . . . .  500,000
Pacific coast—lignite . . . .  500,000

 Total . . . . . .   50,512,000

The area of the New Brunswick coal field is very large, but there is only one thin coal bed, too small to work. Nova Scotia produced 411,541 tons of coal in 1873, and Cape Breton island 639,926. The coal is all bituminous and of a fair quality for gas and steam purposes. There is also an unproductive anthracite coal field in Rhode Island and Massachusetts.—The foregoing fields comprise all the carboniferous coal in North America, and it is not probable that any other districts of any extent containing true coal will hereafter be discovered. Near Richmond, Va., is a very deep coal basin of the triassic age, which was the first worked in the eastern states, and after a long suspension work has lately been resumed. There are two other similar small basins in North Carolina, on Deep and Dan rivers, but neither of them is wrought.—Besides the foregoing carboniferous and triassic coal fields, there is in the N. W. part of this continent a very large area of coal fields which should be described with some detail. The coal or the combustible matter of these western basins is of the kind generally called lignite, of an inferior quality and of a more recent age, the tertiary. It has however the same appearance, and is by its chemical composition true coal; and its distribution in extensive basins along the eastern base of the Rocky mountains, bordering immense treeless plains where no other combustible of any kind can be found, gives to these coal fields an immense value. Indeed, in regard to the population of the gold-mining countries of the Rocky mountains, and to the building of railroads across the plains from the Missouri to the Pacific, the lignitic basin of the west is for the future as important as are for the present the Appalachian coal beds or the coal fields east of the Mississippi river. Along the Missouri river and west of it, the true carboniferous formations sink and disappear under the Permian. The line of the 96th parallel of longitude, from the point where it enters the state of Iowa to the southern limits of Kansas, shows nearly exactly the limits of the old coal fields. Further west the Permian, following a gradual westward dip, is overlaid by the cretaceous formations, which reach a thickness of 2,500 ft. or more; and over these, nearer to the mountains, the tertiary measures appear with their numerous and as yet scarcely explored beds of lignitic coal. By the upheaval of the Rocky mountains, the lower tertiary has been thrown up, sometimes to the perpendicular all along the base of the mountains, and there the capacity of some of its beds of coal has been exposed and is already utilized by workings on a comparatively large scale. The whole lignitic basin may be, like the coal fields of the east, subdivided into different basins, not by any positively marked difference in the nature and composition of the lignitic coal or by any difference whatever in the formation of their coal beds, but merely by geographical limitation, as follows: 1. The New Mexico lignitic basin. It is especially of great extent and rich in coal beds along the Rio Grande, on both sides of it, S. of Santa Fé and Albuquerque as far down as Fort Craig, the supply of fuel for the fort being obtained from a bed of lignite 5½ ft. thick, 5 m. E. of Don Pedro. A number of other valuable beds have been reported near San Felipe, and still more abundantly northward, around Santa Fé and up to the Eaton mountains. The coal of Placiere mountain, which is partly anthracite, is 5 to 6 ft. thick. The following section, taken at the foot of the Raton mountains, shows the average distribution of the lignitic formations of this southern basin:

    Ft.  in.
 1.  Sandstone and shale, space covered  60 0
 2. Soft shale and clay 35 0
 3. Outcrop of lignite showing  2 0
 4. Soft shale and fire clay 26 0
 5. Outcrop of lignite, thin  1 0
 6. Hard gray shale with fossil plants 30 0
 7. Hard sandstone in bank  6 0
 8. Soapstone shale  2 0
 9. Lignite, outcrop, good  2 0
10. Fire clay and shale 36 0
11. Lignite, exposed  2 6
12. Fireclay  6 0
13. Soft shale 30 0
14. Lignite bed opened  4 0
15. Ferruginous and shaly sandstone 50 0

This section rests upon a series of hard coarse sandstone, remarkably mixed with fragments of marine weeds and pieces of bark and of wood, marking this formation as the result of marine deposits along the shores. This, like the alternation of the strata marked upon the above section, especially the deposits of fire clay under each bed of lignite and of shale and shaly sandstone above, gives to the distribution and composition of the lignitic strata an evident likeness to those of the old carboniferous measures. From Trinidad or from the Raton northward to the Spanish peak a number of coal beds have been reported from the same basin as far north as Chicosa, 20 m. from Trinidad. The coal of this country is of a remarkably good quality, some being compact enough to furnish hard coke by distillation, and others producing by the same process a large proportion of illuminating gas. 2. The Colorado lignitic basin, from Pueblo to Cheyenne, covers a wide field, but is to the south at least broken into small isolated areas. One is in the Arkansas valley, E. of Cañon City, with beds of excellent coal, varying from 6 in. to 8 ft. A small basin E. of Colorado Springs has as yet given mere indications of coal in thin beds of 2 to 3 ft. But further north, and from the North fork of Platte river to Cheyenne, the lignitic measures follow the base of the mountains nearly without interruption, furnishing an abundance of fuel to the already large population of the country and to the railroads. Beds of lignite have been opened near the canon of the South Platte, 5 ft. thick; then in a continuous direction northward, near Green mountain, 7 ft. thick; and at and around Golden, from 4 to 11 and even 14 ft. thick. Five miles N. of Golden, on the Ralston creek, a coal vein is worked averaging 16 ft. in thickness without any parting. Still further N. toward Marshall's a number of beds have been tested varying in thickness from 5 to 9 ft.; and at Marshall's numerous beds have been tested and some worked, varying in thickness from 4 to 11 and 14 ft. Beds of the same kind and of equal thickness are worked still further N. and E. on Boulder creek, Erie, Thomson creek, and Cache la Poudre river. Thus the continuity of the basin appears to be ascertained from the North Platte to near Cheyenne. In width the measures appear to be continuous from the base of the mountains to the Platte, about 15 m. from W. to E. There they pass under more recent formations, and of course may be reached by shafts further E. It is to be remarked, however, that the coal becomes less compact and therefore more subject to disintegration by atmospheric influence, and even liable to spontaneous combustion, in proportion to the distance from the base of the mountains. 3. The lignitic basins along the Union Pacific railroad from Cheyenne to Evanston. On this line the first lignite basin is exposed at and around Carbon. It is of small area, but its beds are thick and the coal of good quality. From Carbon, over lower formations, the railroad passes to a new tertiary and lignitic basin with some thin beds exposed, at Creston, Washakia, &c., and then to a rich productive lignitic region in entering Bitter creek and following it from Black Butte to Rock Spring. At Black Butte three beds of coal are exposed, one of which is worked 8 ft. thick. At Rock Spring an upper coal of excellent quality is worked near the surface, 8 ft. thick, and a lower coal, equally good but only 4 ft. thick, is worked 2 m. E. of the village. A boring made at Rock Spring for the purpose of obtaining fresh water has exposed the remarkable development of the tertiary measures in this country. Below the main coal the record of the boring indicates 41 ft. of lignite in 700 ft. This is about the same amount of coal indicated at Marshall's in a section of about 500 ft. of measures. From Rock Spring to Evanston, a distance of 130 m., an upper tertiary formation, mostly of shale, overlies the lignitic. It has no coal; but some of its beds of shale are so bituminous that in some localities they are worked and used for fuel. Evanston and Coalville are the two last localities where lignite beds have been opened for the use of the Union Pacific railroad. At Evanston the Wyoming coal company works the bed 14 ft. thick, interlaid by three slate partings of a few inches each. The Rocky mountains coal company, adjoining the first, has the same bed of a greater thickness, 43 ft., interlaid with numerous beds of clay and shale. This lignite bed is comparable in its productiveness to the great mammoth bed of the anthracite of Pennsylvania. It however occupies a very limited area. The Coalville beds, at a short distance from Evanston, have been considered by some as identical with the Evanston deposits, and by others as from an older formation, the upper cretaceous. The northern lignitic basin was the first dis- covered and recorded in the history of the United States. It is however far less known than the others, being as yet out of the lines of travel and emigration. The so-called lignitic formations were first noticed in Lewis and Clarke's expedition to the Rocky mountains while ascending the Missouri river in 1804. The coal was observed by them at various points from above the Mandan village in ascending the river for a distance of 990 m., and along the Yellowstone river in descending it from about lat. 45° to its mouth, lat. 48° 20′. More recent expeditions in the same country, especially the surveys of Profs. Meek and Hayden, have recorded the same wide extent of area of the N. W. lignitic field and the richness of its coal products. Dr. Hayden in 1857 published a map with sections of the country bordering the Missouri river, accompanied by explanations and documents of the highest scientific interest. This work embodies the results of three years' explorations by the author in the northwest. It marks the outlines of the northern lignitic basin on both sides of the Missouri from below Fort Clark to the Muscleshell river, the northern limit marked by British America and the southern by the head waters of Cherry creek and the Black Hills, narrowing between the Black Hills and the Big Horn mountains, and descending further south to the North fork of the Nebraska river. The author estimates the area of this basin at 400 m. in length and 150 m. in width, or about 60,000 sq. m., which estimate however he rightly considers too low. The most important localities on the Pacific coast where lignitic coal has been produced are Mount Diablo near San Francisco, Coos bay in southern Oregon, Seattle on Puget sound, Bellingham bay in Washington territory, and Vancouver island. It is also found in Alaska and elsewhere, and there is anthracite on Queen Charlotte's island.—Measured by the amount of their annual production, the most important coal fields out of the United States are those of Great Britain, which produce about one half of all the coal mined in the world. The whole quantity of coal produced in the kingdom since it was first used in the country is estimated at 4,672,090,988 tons, of which the production of the year 1873 was 127,016,747 tons; 86 per cent. of the production of that year was from England, and the anthracite was less than 1,000,000 tons. The quantity of available unmined coal has been ascertained by a royal commission. The resources of coal in the kingdom, amounting to 90,207,000,000 tons in 1871 according to this report, are generally thought to be exaggerated by including the small seams down to one foot in thickness and those below 3,000 ft. in depth, which is probably as deep as coal can be mined, instead of 4,000 ft., as given in the report. The South Wales coal basin has the largest area and much the largest quantity of unmined coal, about 36 per cent. of the whole, but the largest production is from Durham and Northumberland, or the Newcastle coal field. The quantity of coal in Scotland is comparatively small, and in Ireland unimportant. Great Britain exports about 13,000,000 tons annually, and has for many years supplied the world with vast quantities of manufactured articles made with the aid of her coal. The following tabular statements contain much important, useful, and accurate information. The coal produced in 1873 was used and disposed of as follows:


In the manufacture of iron 35,119,709
In steam power in manufactories 27,550,000
Domestic or household consumption 20,054,000
Exported to foreign countries 12,712,222
Used in mines and collieries 9,500,000
In the manufacture of gas 6,560,000
In steam navigation 3,650,000
In glassworks, potteries, and brick and lime kilns  3,450,000
On railways 3,790,000
In chemical works and all other manufactures 3,217,229
In smelting other metals 763,607
In water works 650,000

 Total production of Great Britain in 1873  127,016,767


 miles of 
Thickness of
 No. of beds 
of coal.
of coal.
Millions of
 tons within 
4,000 ft.
 Tons of coal 
in 1873.

Durham and Northumberland 460  ft.  2,030 ft. 16 ft.  46 ft. 10,037  29,640,397
Cumberland 25 2,000  9 36 405  1,749,036
Derbyshire and Nottinghamshire
217  6,000  3 62 5,546 
Shropshire and Anglesea  9 1,309  8 36 1,570,000
N. Staffordshire 75 5,000 30 150  3,825  3,892,019
S. Staffordshire and Worcestershire  93 1,810  6 65 1,906  9,463,559
North Wales 47 3,000  7 30 2,005  2,450,000
South Wales
906  12,000 25 84 32,456 
Forest of Dean 34 2,765  8 22 265 
Bristol 150  5,125 20 71 4,218 

 Total of England 2,821 80,208  110,055,552 
Scotland 9,843  16,857,772 
Ireland 156  103,423 

 Total Great Britain 90,207  127,016,747 

—France has a large number of small detached coal basins. The basin of St. Étienne, in the department of Loire in S. E. France, has the largest annual production, about 3,500,000 tons; the basin of Valenciennes in the north, an extension into France of the coal field of Belgium, produces nearly as much, and that near Calais almost 3,000,000 tons. These and three or four others in S. E. France, each yielding about 1,000,000 tons per annum, produce the bulk of the coal of that country. The whole production of France in 1872 was 15,899,005 tons, and in 1873 about 17,500,000 tons. The annual production of anthracite is about 1,000,000 tons. The following tables give the most important statistics in regard to them, derived from the report of a late French parliamentary commission in 1874:

KINDS. No. of

Tons in

Bituminous  319 1,527  52 14,459,273  90.94
Anthracite 146 221  24 1,006,525   6.33
Lignite 147 338  24 433,307   2.73

 Total 612  2,086   100    15,899,005   100.000  


 Bitum.   Anth.   Lignite.   Total. 

Worked 1,434  204 74 57 335
Not worked 652  115 72 90 277

 Total  2,086  319 146  147  612

Germany is the largest coal-producing country in continental Europe. In 1872 the coal production of the empire was 42,324,466 tons, of which Prussia proper produced 36,973,411 tons; and there was a considerable increase in 1874. Less than one fourth of the whole product, 9,018,048 tons, is lignite or brown coal. The largest production was in the Rhine provinces, 11,500,000 tons; Silesia, 10,500,000; Westphalia, 10,000,000; and Saxony, 9,500,000. About two thirds (6,139,851 tons) of the brown coal comes from Saxony, where also about 3,000,000 tons of true or carboniferous coal is mined. Belgium is the next in rank as a coal-producing country, having mined 15,658,948 tons in 1872; the two principal districts are those of Liége and Hainaut. Austria mined 10,389,952 tons in 1872, more than half of which (5,676,672 tons) was brown coal. Nearly half of the whole product (5,098,080 tons) came from Bohemia, 1,500,000 from Hungary, and nearly as much from Styria. Nearly all the provinces produce both black and brown coal, or carboniferous coal and lignite. Russia has a large coal area, which like that of Scotland is subcarboniferous, or situated geologically below the formation in which the best coal of England and America is found. The only coal field of Russia belonging to the true coal formation is a small tract in Poland containing 80 sq. m., producing one third of the whole amount mined, which was 1,097,832 tons in 1872. Some good anthracite is reported near the sea of Azov, of which 331,896 tons were produced in 1872. Russia also produced in the same year 27,586 tons of lignite and 738,350 tons of bituminous coal. Spain has a good coal field of the carboniferous age, measuring 3,501 sq. m., but the production was only 570,000 tons in 1872. There is also coal in Portugal, the production in 1872 being 18,000 tons. The coal of New South Wales in Australia is believed to be true coal or carboniferous, not a lignite. The amount mined in 1873 was 942,510 tons, but the product does not increase rapidly, as it was 919,522 tons in 1869. The coal in Italy is lignite or later than the carboniferous age, as is also that of India, covering an area of 2,004 sq. m., and those of China, Japan, New Zealand, and South America, except some true coal in Brazil.


of coal.
 Year.   Production 
in tons.

United States 192,000  1873 50,512,000
Nova Scotia 18,000  1,051,567
Great Britain 11,900  127,016,747
France 2,086  17,500,000
Belgium 900  1872 15,658,948
Germany 1,800  42,324,466
Austria 1,800  10,389,952
Russia 30,000  1,097,832
Spain 3,501  570,000
Portugal ...... 18,000
Australia ...... 942,510
India 2,004  500,000
Chili, China, Japan,
 New Zealand,
 and all other countries
 (estimated) ...... .... 1,000,000

  Total ...... ....  268,582,022

—The early history and development of coal is very obscure. It appears to have been used by the ancients only to a limited extent. Theophrastus, in his treatise on stones, mentions lithanthrax as used by the smiths of Elis. But the Romans, who excavated several of the ancient aqueducts of France through the coal measures, developing beds of coal, paid no attention to the mineral. The first notice we find in official records of the development of coal in England, the first country in which the mining of coal became a commercial industry, is the receipt of 12 cart loads of “fossil fuel” by the abbey of Peterborough in 850. But evidences exist to prove that coal was used to a very limited extent by the Britons before the Roman invasion; and the discovery of tools and coal cinders near the stations on the Roman wall, indicates that they must have learned its use from the Britons. The first evidence, however, of regular mining operations is found in the books of the bishop of Durham, by whom in 1180 several leases were granted for mining “pit coal,” a term since common among the English miners and writers on coal. The coal of Belgium appears to have been developed about this time, or during the 12th century, near Liége. It is said that a smith named Houillos first used coal in the village of Plenevaux, near that place, about this time, and in commemoration of this discovery the French name of coal is houille. Coal was first used in London in 1240; and in 1300 considerable quantities were made use of. A tax of from 1s. to 10s. per chaldron was imposed on coal in England during 400 years, ending in 1803. The first attempt to make pig iron with pit coal appears to have been in 1612, when a patent for this purpose was granted to Simon Sturtevant, but it was unsuccessful. Dudley also obtained patents in 1619 for the same purpose, but also failed, and was imprisoned for debt in consequence. The first successful effort appears to have been made by Mr. Darby of Coalbrookdale in 1713; and in 1747 cast iron suitable for cannon is said to have been made at this place, both the coal and iron ore used being taken from the same mine. In 1700, 64 furnaces were in blast in the forests of England, producing about 20,000 tons of pig iron annually; in 1788, only 13,000 tons of charcoal iron were made, and 61,300 of pit coal or coke iron; but during 1870, 5,963,515 tons were made with coke and coal. The aggregate steam power of Great Britain in 1860 was 38,635,214 horse power, equal to the productive laboring force of 400,000,000 men, or twice the power of the adult working population of the globe. Nothing more striking or instructive, in regard to the value of coal when utilized by an industrial community, could be stated than this fact.

AmCyc Coal - United States fields.jpg
Engd/. by A. Petersen, Washington, D. C.