The coal formation is remarkable for the peculiar appearance (facies,) of its micaceous sandstones and its argillaceous shales. In the coal sandstones, the elements of feldspar and quartz, in very nearly equal proportions, spangled with mica in little scales, passing in the lower portions, into breccias and conglomerates with large fragments, are evidently the result of the action of the waters upon pre-existing transition rocks. The granites and gneiss have furnished the principal amount of these elements; and we can often determine the points from whence they have been drifted. The argillaceous schists, rarely soluble, but always falling to pieces in the air, form the passage of the transition argillaceous schists into the true clays of the posterior strata. They are evidently decomposed parts of the rocks which constitute the sandstones. An impure melange of kaolin, of silex and of mica, of which the elements, fine enough to have been held in suspension, were only deposited when the stagnation of the waters permitted. These beds alternate with a great predominance of the sandstones; all are frequently colored by the disseminated carbon, which gives to the ensemble a grey tint and a characteristic duskiness. The presence of the carbon manifests itself also by that of the carbonate of iron-fer carbonaté lithoide -which is found, either in subordinate beds, or in disseminated nodules rognons-in certain beds of clay. Finally, it manifests itself by numerous vegetable impressions, and by the frequent, but not essential, presence of seams of coal, sometimes fat and sometimes dry.

The influences which have determined the characters of the rocks that are associated with the coal beds, have been so constant, that not only are they identical all over the globe, but in the cases where coal beds are found in other formations than the coal formation, the rocks of those formations abandon their special characters to borrow those which we have described.

Thus, in the anthraxiferous formation which immediately precedes the coal period, the lean coals which are worked in the west of France, are accompanied by feldspathic, micaceous sandstones, and carbonaceous schists, with impressions of calamites, ferns, and sigillariæ. Black argillaceous schists, with nodules of carbonate of iron, accompany equally the beds of secondary coal which are found in certain points of the lias near Milhau, (Aveyron) and in Yorkshire. To sum up the various geognostic positions of coal: they are met with, 1st, In the anthraxiferous formation; that is to say, in the upper part of the transition series, even above the silurian beds. 2d. In the coal formation, properly speaking. 3d. In the marnes irisées, where are found the coals of Noroy and Gemonval. 4th. In the lias formation. [Environs of Milhau.]

Above this last position, the vegetable debris is found most generally in the state of lignites. We find, but rarely, in the lignites of the cretaceous and tertiary formations, portions from which the ligneous texture has disappeared, and which present the appearance of coal; but this case is exceptional. Thus certain lignites in the

environs of Marseilles, and others which exist in the tertiary beds of Italy, present the tissue and the characters of coal, but these accidental facts, which establish between the coals and the lignites mineralogical transitions that exist even between rocks the most distinct, strikes no blow at the rules of position, established undeniably by geological observations. It is the same with that other geognostic law which assigns peat solely to the alluvial epoch, or the actual existing epoch.

The meagre coals and anthracite appear in general to be of a more ancient age than the fat or flaming coals. This classification is sufficiently indicated by the general dry nature of the combustibles mined in the anthraxiferous formation of the west. In the north, the lean coals of Fresne, Vieux-Condé, Vicoigne, are evidently inferior to the fat beds of Anzin and Denain. The beds found in the carboniferous limestone at Château l'Abbaye are true anthracites. The anthracites. of the environs of Roanne, and those of the United States,* belong to the upper formation of the transition series. But it is necessary again, more than in the preceding cases, to abstain from taking this rule in an absolute manner; for the anthracite state is very often the metamorphic state of the coal, and even of the lignites. The interesting researches of M. Elie de Beaumont upon the anthracites of the Alpine regions have demonstrated this fact, otherwise easy to conceive.'

From each of the four classes or epochs of combustibles, M. Régnault has selected the most characteristic, and after having submitted them to analysis, he has acknowledged that this general succession of characters in the fossil combustibles is in accordance with a successive approach towards the composition of the vegetation; in such manner that, from the anthracites of the transition series, even to the lignites and to the peat of the existing epoch, the fossil combustibles form a series of which almost pure carbon forms the base, and which is gradually charged with four, five, and six per cent. of hydrogen, and with four, eight, twelve, sixteen, and thirty per cent. of oxygen.

We may lay down this principle, abstraction being made for the anomalies of metamorphism, that the more of gas that a combustible contains, and the higher the amount of oxygen and hydrogen, so much the more modern is the combustible.

LOCAL POSITION AND ARRANGEMENT OF BEDS OF COAL.

Coal, whatever may be the formation in which it is found, affects the form of beds, of very variable thickness and continuity, but whose

Respecting the geological age of the anthracite of the United States, we think that there is good ground for dissenting from the views of M. Burat, in placing this carboniferous formation in the superior part of the transition series. It is true, the present writer formerly held and advocated precisely the same opinions, but subsequent investigations have clearly established the geological fact, that the Pennsylvania anthracites are simply in the metamorphic state; that they are based upon the old red sandstone, and that the numerous basins in which they are deposited are but isolated, or out-lying portions of the great bituminous coal field of the Alleghany Mountains.

constant character is that of conforming to all the courses [allures] of the beds of schist and carboniferous sandstones between which they are included. This stratification is not only indicated by the limits of the roof and the wall or floor, but also by natural variations in purity, the positions of which generally pursue or occupy lines parallel to those of the roof and floor; by the bands of intercalated slate, and by the continuous barres which divide the beds into several courses. Finally, the coals themselves often present a great number of interruptions, and of veins which render its structure striped, lamellar, and following the direction of the stratification.

The stratification of coal ought not, however, to be considered as absolute, and to be compared to that of the calcareous or argillaceous beds of the sedimentary formations, nor even to that of the sandstones and shales which alternate with them. Certain beds present massive undulated forms, yet without these undulations having been occasioned by the course or strike of the formation. This shows that the origin of the coal permits, at one and the same time, thin layers, continuous and of the greatest regularity, and thick beds, so limited and irregular, that they may be assimilated to masses. The ulterior details, respecting the forms and courses of the principal coal deposits, will decide perfectly our ideas in this respect. The thin and • regular beds, although very much disturbed, of the basins of the north of France and Belgium, and the thick and limited beds of Montchanin represent the two extremes of position.

The number of coal beds in the same formation, as well as their thickness and continuity, appear to be subject to very great variations. Nevertheless, there is a certain connection between these different conditions. The thin and regular beds are .commonly continuous and multiplied; the thick and unequal masses are, on the contrary, limited in their extent, and there are rarely more than two or three superposed in the formation which encloses them. Thus, in the basin of Mons, in Belgium, more than one hundred distinct seams of coal are counted, whose ordinary thickness varies from eight inches to near five feet. In the collieries of the department of the North, in France, there are few centres of exploitation which do not count six, eight, twelve, or more beds of coal; but their maximum thickness does not exceed three feet, and the greater part of those which are worked have only about twenty inches.

Although coal beds have frequently been traced along a distance of many miles, yet we ought not, even in the case of very great regularity, to suppose that certain beds of coal are absolutely coextensive with the whole formation. For example, there is an interruption between Valenciennes and the Belgian frontier, to such an extent that the beds of Anzin are not those of Mons, and these again have no relation of continuity with the beds of Liege or Charleroy. The same remarks can be applied to other coal basins. Thus, in the basin of the Loire, the beds of Rive-de-Gier are not the same as those of Saint-Etienne. We may then, in a basin of some extent, consider the coal as forming, within the beds of sandstones and shales, special

districts; often isolated, the one from the other, by sterile portions, and of which the coal beds, differing in number and power, have no relation of continuity.

Although, then, even if we have discovered the sandstones and the shales of the coal formation, it does not follow that we have also found the coal, though we were on the prolongation, in direction or inclination, of known beds. To form a probable hypothesis on this subject, it would be necessary first to study the peculiar conditions of the formation on which to operate, and calculate, from the known portions, the chances that we may have.

The strata of the basin of the Saône-et-Loire appear to form basins subordinate to the principal basin, which is filled up with coal, sandstones and schists. These subordinate basins are bounded like the basin which contains them, and have, besides, nearly similar proportions between the axes. Further, the coal appears there to diminish in length in proportion as it acquires thickness. In the valley of Creuzot, the great bed which is worked has twelves metres, or forty feet, of mean thickness. In the enlarged portions it has 40 metres, or 130 feet from wall to roof. In direction it is not prolonged above 2000 yards; and, with regard to its limits, its divided extremities, there impoverished, present all the symptoms of a total suppression.

The bed to Montchanin, greatly inclined, whose thickness attains even to 70 metres, or nearly 230 feet, measured from roof to floor, representing, consequently, the thickest known coal bed, is equally one of the most limited in extension. In fact, in the upper part of the exploitation, this direction is about 650 yards, at the end of which the bed terminates abruptly, and is confused or entangled in the rocks of the roof and floor. At a lower stage, about thirty yards below the first, the length is reduced to 450 yards, and it is probable that at the depth of about 150 yards the bed will terminate.

The basin of the Loire contains, in the region of Rive-de-Gier, but three beds, of which the average united thickness does not exceed 32 feet; but, in the district of Saint-Etienne, the sum of the regular beds amount to 114 feet, in fifteen to eighteen beds. At Brassac they amount to from 27 to 40 feet; 45 feet at Comentry and Doyet; and 48 to 65 feet in the basin of Aubin. It is remarkable that, in all these basins, the coal beds, of 15 to 30 feet, are occasionally reduced, by contractions, to 6 or 10 feet, and at times are swelled out to the thickness of 60 to 90 feet, an ordinary and normal fact.

In the department of the North, on the contrary, 30 feet of total thickness are divided into 14 beds, worked at Fresne and VieuxCondé. The 12 beds of Aniche only form 22 feet; four successive beds at Douchy have only 11 feet aggregate; at Denin 73 feet only; and 38 feet are occupied by not less than eighteen beds at Anzin. There are also still more veins, which are unworked, and whose thickness is below one foot each. But these beds are regular and prolonged, and are not disturbed by those enlargements and entanglements so frequent in the beds of the southern basins.

This difference of power and continuity in the coal beds agrees

also with some very important differences indicated by geological observation.

The southern basins of France appear to have been deposited, · during the coal period, in isolated lakes of fresh water; encircled, and entirely commanded by the neighbouring summits, from whence the materials have often been drifted with violence: forming breccias and conglomerates. In studying this debris, especially in the lower parts of the deposit, we can recognize the transition rocks of the surrounding countries. The northern basin of Belgium and France, containing at its base the carboniferous limestone, is, on the contrary, only composed of sandstones and fine schists. It appears, from the character of the fossils, to have been formed in marine waters, and thus represents, with the coal basins of England, the pelagic accumulations of an epoch, of which the basins of the south are but the lacustrine terminations. It is, then, natural to discover, in these northern deposits, a regular and continuous disposition. which comports not with the deposits of the south.

The southern basins, desposited in isolated lakes of fresh water, form the principal riches of France. The aggregate thickness of the coal is, besides, nearly as great as in the basins of the north. To sum up all, we can lay down no absolute rule for the number and power of the beds of coal, any more than for their continuity. The indices, which result from the direction of the stratification, have, nevertheless, a real value, even in the countries where the continuity presents the most frequent exceptions; because they always conduct to the possibility of finding, if not the prolongation of the beds, at least to formations analogous to such as have been already discovered.

ACCIDENTS, FAULTS, AND IRREGULARITIES, OF COAL BEDS.

The beds of coal are rarely in the position where they have been produced, for that position would approach sensibly to the horizontal; a condition compelled, if not by the mode of production of the coal itself, at least by that of the beds of sandstone and slates between which it is stratified. Most frequently, the uniformity of the formation is disturbed, not only by inclinations, more or less great, but also by the folds which change these inclinations, and distort the beds to such an extent that a vertical shaft might cut them several times. There often, also, prevails one or several systems of faults [failles] which change the levels and isolate, one from the other, the divers parts of a bed.

This accidentation, subsequent to the production of the beds, and resulting from dynamic perturbations, commonly influenced by determinable conditions of direction, must be distinguished from the contemporaneous accidents inherent even to the production of the coal; such as the undulations of the roof and floor, which swell or contract a bed, and the intercalations of layers or of amygdaloid rocks, which interrupt the regular order of the stratification. Nevertheless, there is an evident connection between these two causes of irregularities;