umn, will produce 70,884 cubic feet in, 5 equal and similar parts; 94,850 cubic feet, in 10 equal and similar parts; 99,772 cubic feet, in 15 equal and similar parts; 101,132 cubic feet, in 20 equal and similar parts.

Elaborate arrangements of this character are not necessary in the coal mines of Ohio, because of their comparative freedom from firedamp; but they will become necessary some day, when the mines are opened on the lower coals, near the center of the basin, as the fire damp will be given off abundantly. The main objects to be kept in view in the present state of mining, consist in the proper and timely construction of a furnace, fan, or other ventilating power, and in proper and timely arrangements for the distribution of the air. Neglect of these matters lies at the bottom of all the bad air of mines in the State.

As the furnace still retains a decided preference among practical men, the laws which govern it should be carefully studied and well understood by the mine superintendents. A mistake cannot be made in constructing a large furnace, and coal is both abundant and cheap at a coal mine. The grate should be from four to six feet in length, the height above the bars should not be less than three feet, and there should be at least two feet below. Every upcast shaft should have at least thirty feet of sectional area, and be made dry with incombustible lining. Water falling down an air-shaft, or running down its sides, greatly impairs the force of the air current. But no matter how well a furnace may be constructed, nor how carefully the upcast may be maintained, coals will be burned to no purpose if the air-courses are not properly constructed, and made large and roomy. Spacious air passages will admit of the easy and abundant flow of air.

There may be many times the amount of air passing into a mine and returning by the upcast, and yet the miners be suffering for want of a healthy ventilation in their working places; and this fact was frequently met with in many mines. The air-courses were either too far behind, or the air was permitted to leak and split at every door and stopping, until the whole of the current was lost before it reached the miners, whose lamps were burning dimly-sometimes even their combustion could only be maintained by hanging the lamp downwards-and the men themselves were gasping for breath, so to speak, in an hourly thickening atmosphere.

Since the mining commission examined the leading coal mines of the State three years ago, a very marked improvement has taken place in ventilation, particularly in the Tuscarawas valley. I found many cases where old furnaces had been torn down, and more powerful ones put in their places; in some cases two furnaces were in operation. The stop

pings had also been more carefully watched and kept air-tight, and the air-ways themselves kept well up to the faces of the workings. Many of the more thoughtful and intelligent of the responsible managers are now driving double entries, which are always kept abreast, from which airholes are cut from the one to the other, and securely stopped, as newer ones are made, thus delivering the current of air to all the entry faces.

THE COAL RESOURCES OF THE STATE.

The Coal Measures of Ohio form part of the great Alleghany coal field, which extends through portions of nine States-Pennsylvania, Ohio, Maryland, West Virginia, Virginia, Kentucky, Tennessee, Georgia, and Alabama, and includes an area of fully fifty-five thousand square miles, being upward of seven hundred miles long, and averaging nearly eighty miles wide. The State of Ohio contains more than ten thousand square miles of the most favored portion of this field-the coal area extending from Geauga county on the north, to Lawrence county on the south; and from Jefferson county on the east, to Holmes county on the west.

There are no less than ten different minable beds of coal in the State; they do not all, however, extend over the whole of the coal area, for the Alleghany coal field, in common with all other coal fields, possesses a basin shape; hence the lower seams occupy much greater areas than the upper ones. The deepest place (the basin) of the coal strata is on the Ohio River, between Bellair and Pomeroy. At this point the coal-bearing rocks are from fourteen to fifteen hundred feet thick, and inclose all the seams of the series. North and west from the basin the rocks rise toward its margin, and one after another of the different coals crop out, till reaching the extreme outcrop, the lower coal of all-the famous Briar Hill seam-comes to the surface and disappears forever.

Although the absolute slope and structure of the coal field of Ohio has been ascertained with remarkable accuracy by the late careful and able Geological Survey, the estimates made of the amount of available coal are beyond all question too high. Borings made in different parts of the coal area for oil, salt, etc., as well as examinations made along the flanks of the several seams where they crop out, or come to grass, in deep surface erosions, show that few of the lower coals are persistent, and that a coal of a minable height in one region is frequently found too thin in another region to make it of any immediate or prospective commercial value. The coal of some seams appears never to have been deposited over parts of certain areas, or to have been wholly removed, after deposition, by denudition. Besides, our coal beds, in common with all coal beds, from whatever field in the world, are subject to rock-faults, horse

backs, and other mining troubles, which give cause for quite an item of subtraction.

Although our coal area includes ten thousand square miles-equal to that of Great Britain, it does not follow from this fact that we possess an equal amount of available coal; for the Coal Measures of Ohio are nowhere more than fourteen or fifteen hundred feet thick, while the Coal Measures of England in some districts-that of South Wales-are fully ten thousand feet thick, though coal can never be mined at half that depth. Taking, however, four thousand feet as the available mining depth, the limit at which the Royal Coal Commission of 1871 puts it, and the coal area of that country is still more than double that of ours. The thickness, and number, and quality of the beds must also be considered equally with their extent of area, in forming comparisons of this nature. Our thickest coal, that of the great vein of Hocking, Athens, and Perry counties, nowhere exceeds twelve or thirteen feet in thickness, while the ten-yard coal of Dudley, Wolverhampton, and Billston, in England, is from twenty-four to thirty-six feet thick. The maximum thickness of our coal may be stated at forty-five feet; in the North Staffordshire district they have one hundred and forty feet, and forty different beds of coal, seams of two feet and under not being considered. But so far as quality is concerned, we have no comparisons to fear.

In his recent work on Coal and Coal Mining, Warrington Smyth considers the amount of available coal in the British Isles at eighty billions tons, Edward Hull, of the Geological Survey, having several years previous made the same statement, the depth of mining being calculated at four thousand feet. The Coal Commission puts the amount at ninety thousand two hundred and seven millions tons as proved coal, and adds fifty-six thousand two hundred and seventy-three millions tons as having a probable existence at workable depths (four thousand feet), under the Permian and New Red Sandstone formations. Some years ago Mr. Henry Hussey Vivian made the extraordinary statement in the House of Commons that, not only was four thousand feet not the workable depth of coal mining, but that twenty-four billions tons could be raised from the South Wales coal fields alone at a greater depth than four thousand feet.

The deepest mines in England are the Pendleton pit, which is two thousand two hundred and fourteen feet deep, and the Rosebridge pit, two thousand three hundred and seventy-six feet deep. A pit at Charleroy, in Belgium, is two thousand six hundred and forty-nine feet deep, and another has been sunk, but is not working, to three thousand feet deep. Warrington Smyth, on the authority of Prof. Trasenster, of Leige, puts

the depth of the Belgium mines at much greater depth, respectively two thousand eight hundred and twenty feet, and three thousand four hundred and eleven feet, but he is evidently mistaken.

Before even four thousand feet of workable depth is practicable, some other means of ventilation will require to be discovered and applied to coal mining. The heat of a mine increases about one degree of Fahrenheit's scale for every sixty or seventy feet of descent; at three thousand feet the temperature would be one hundred and two degrees, and at four thousand feet one hundred and twenty degrees. Rapidly moving currents of air may cool the working faces several degrees below these figures, and compressed air may still further cool the temperature, but no miner can work to any advantage in a temperature exceeding eighty degrees. The ten minable beds of coal of Ohio will aggregate forty to forty-five feet at many points on the Ohio river. As, however, the upper coals, by reason of the basin slope of the field, occupy but limited areas, and no coal seam, not even the lowest, extends over the whole of the coal area, a very heavy discount must be made in forming any estimate of the average thickness applied to the whole coal area. Nine feet will approximate it, and when due allowance is made for waste by crushed and lost pillars, and small coal lost in screening (being at least one-third of the whole), there is left but six feet of merchantable coal. This estimate would give sixty-two billion nine hundred million tons as the aggregate commercial yield of Ohio, which, at the present rate of consumption, would require a period of twelve thousand five hundred and ninety-two years to consume it. It would supply the whole of the United States seventeen hundred years, and Great Britain nearly five hundred and eighty years, were no yearly increase made to their outputs.

The main mining centers in Ohio are the Mahoning valley, the Tuscarawas valley, the Hocking valley (including Straitsville and Shawnee), Salineville Bellair, Steubenville, Pomeroy, Ironton, Coshocton, Cambridge, and Letonia, in addition to many other important mining districts along the lines of the several railroads which traverse the coal fields.

The coals which lie in the northern and western flanks of the coal area are more eagerly sought for and mined than those of the more central part of the field, as they distance competition in the supply of the great coalless area lying to the north and west. In most cases, too, these coals are of very superior quality.

The mines of the Mahoning valley, the Tuscarawas valley, and the Jackson and Steubenville regions, are mainly shaft openings, the coal being generally below water level. The openings of the Hocking valley, the Pomeroy district, the Cambridge, Coshocton, and Ironton localities

are drift mines, the coal being reached without sinking. In some of the regions, where the strata dip rapidly, as at Bellair, part of the mines are level free, and part are shaft openings.

Although the Coal Measures dip from the flanks of the coal area towards the basin of the great Alleghany coal field, this dip is by no means uniform throughout. The strata sometimes rise along the general line of direction of the dip, forming a synclinal or trough, and then commence dipping again, forming an arch or anticlinal. These folds of the strata, Prof. Newberry says, are due to the same agencies which caused the upheaval of the Alleghany Mountains. In addition to these undulations, there are a multitude of local troughs and arches, some of which are seen in every coal mine in the State, which the miners call "swamps" and "hills." These hills and swamps are, in my judgment, the result of inequalities in the floor of the coal marsh, existing when the original peatbogs, from which the coal is derived, was deposited. In the lower coal-that of the Mahoning valley, the Tuscarawas valley, and the Jackson region, they abound in every coal opening, but they are also met in every seam of the series, the hills generally growing less steep and high as we ascend in the Measures. In the Mahoning valley the coal troughs or swamps are often more than one hundred feet below the level of the upper surface of the "flag rock"-the Waverly sandstone, though I have never seen the coal to rise in the hills to a greater height than sixty or seventy feet before it thinned out. In the second minable bed of the series (Prof Newberry's No. 3), which, along the outcrop of the field in the Mahoning and Shenango valleys is only found in patches, the hills are neither so high nor so steep as in No. 1, but the coal itself rises to heights fully equal to it, and preserves a greater uniformity of thickness, though growing gradually thinner on the hills. In the mines of Coshocton, opened in No. 6, a swamp runs along the face of the coal, from which the strata in some places rise on both sides, at the rate of five hundred feet to the mile. In this swamp the coal is five feet thick, and is divided into two benches by a parting of fire-clay two inches thick, the lower bench being here twenty inches. As the coal ascends the hill, the lower bench grows gradually thinner, till it disappears altogether; then the fire-clay bench is cut out, and still further upward the lower part of the upper coal is thinned away, until the seam has become too low to follow further with profit to the mine operator.

Whether this swamp would be found immediately below on the next seam of coal, and would run in the same line of direction, could only be ascertained by an appeal to facts, of which I had no means at command; but I have observed in other parts of the coal field that such undulations