Everywhere between the beds of coal are strata or layers of other rocks, such as sandstones, shales and clays, which seem to have been left many, many years ago as sediment in the bottom of water. The roof of the coal or rock, just 5 above the coal-bed, as well as the floor, is, as a rule, a shale of hardened mud. These shales, which split very easily, have stamped upon them impressions of leaves and ferns, and even the fossil stems and roots of plants often the relics of lofty trees! If we magnify a thin scale or section 10 of coal, a plant-like structure can be seen. There is a kind of coal, called lignite, or brown coal, which seems to be the link between true coal and living plants. Now and then a trunk of a tree is dug out, one end of which is scarcely changed from wood to mineral matter; the middle 15 of this is brown coal, the other end true coal. Fossil plants in the coal measures vary in kind according to the place of the beds. Those farthest north, such as are in the Greenland coal, are like the plants which grow in Middle Europe.

Marks of ferns are more common than any other plant 20 in the coal measures. The beautiful fronds, or leaves, which, as there are no flowers, bear on their surface the fruit or spores of new plants, are very plentiful. This is not because they were the only plants which grew in those ages long gone by, but because they were so resinous as to 25 be the last to decay. Besides ferns, we can trace in the texture of coal the grain of pine and fir wood, or the conebearing trees; and in the fossil stems, plants like the comOur present ferns and club mosses are pygmies compared with those that lived so long ago, and reached 30 the size of giant trees. Similar lofty tree-ferns now grow fifty or sixty feet high in the islands of the South Pacific Ocean.

mon moss.

From these facts we infer that the coal-beds are a changed state of former vegetation, and that the bitumen of the 35 coal is the altered resin and turpentine, so plentiful in trees

of the fir and pitch-pine family. To account for the great depth and the number of the coal-beds, we may be certain, that every seam was, however far back, a field of vegetation on the surface of the earth, and that every layer of 5 shale or clay, now the floor and roof of the coal-beds, was formed by mud settling down at the bottom of water. So we see that the land has been covered by water as many times, at least, as there are strata or layers of shale; and has become dry again as many times as there are beds of 10 coal. We believe, too, because the plants were tropical and of great size, that the coal countries must have been, at times, much hotter than now.

Fossil remains of animals such as can live only in hot climates, and others which can live in cold climates, are 15 found in abundance in the rocks. The nature of the rocks thus proves that at long intervals the land has had to bear the extremes of heat or cold for ages together.

When we walk in some of our woods we sink up to our knees in the fallen leaves. As these leaves decay, they form 20 a vegetable soil. Every autumn brings down the leaves and adds a new layer to its depths, so that by the time a hundred years have passed by, this soil has become very deep, and in it are buried whole forests of ancient trees! How much higher the trees now growing must be rooted 25 than those which first grew upon the earth!

In Europe there are many peat meadows or bogs. These bogs are masses of vegetation formed of the matted roots of decayed grasses and mosses which die down every year, and of the fresh annual growths that take their place. In 30 the deep Irish bogs are found half fossil trees, called bog oaks, out of which fancy articles are often carved.

The deep parts of the bogs are dense and dark, from the pressure of the soil above, and seem like lignite or coal. Roman pavements have been found ten feet below 35 the surface of some of the European bogs.

Now let us look forward, say, twenty thousand years. By that time the land will have sunk and been heaved up again many times; many changes of layers of sediment and new growths of bogs will have occurred. Then, that 5 which is marshy land stretching out in the sunshine will have sunken deep down into the earth; will have been pressed into a dense substance by the heavy earth above it, and have become only as many inches thick as at first it was yards. Heat and chemical forces, acting upon this 10 through so many ages, will have changed it into the black, shiny mineral which we call coal.

So you see the kind of coal in a bed depends upon the kind of plants or trees that grew upon it when it was at the surface of the earth; upon the amount of pressure above 15 it; and upon heat and time. The giant trees whose roots and stems are in the coal measures show us that the vegetation of the earth, long before man came to live upon it, was in structure something like a moss which now seldom grows more than a foot high.

20 Our coal-beds tell us a great deal about the ancient world and the appearance it must have worn, so long ago that we cannot count the years. We learn from them that part of our country has for many ages past been, at times, as hot as the Tropics, then as cold as the Poles; that it has 25 sometimes sunk below the sea and at other times been raised up high and dry. Learned astronomers have found out and taught us how such changes have been brought about by the movement of the earth with regard to the sun. By-and-by it will be part of our lessons to study and under30 stand these wonders.

A mine of coal is dug out on a very regular plan. When a shaft or pit is sunk down to the bed, the miners do not try at once to get all the coal within their reach, but they cut or drive tunnels, which they call drifts, and as soon 35 as they get a little way in, they cut across drifts right and

left, so that at last the mine consists of narrow lanes or passages, and huge square blocks or pillars of coal are left to support the roof. As soon as the drifts reach the bounds of the mine, the miners remove these pillars, the most dis5 tant ones first, and let the mine fail in; and this is the most dangerous part of their work.

When the mines fall in, it often causes the surface of the earth to sink. In the coal districts it is not uncommon for great cracks to appear in the house walls, for chimneys to 10 lean over, and buildings to fall, from the giving way of the foundations.

Both in driving a passage through the seam and in hewing the coal, the labor is much lessened by the readiness with which the coal splits in certain directions. These direc15 tions are three in number, and are called planes of cleavage.

The first are the planes of the bedding, running even with the roof and floor of the mine. The second and third planes are at right angles to the bedding, they run from roof to floor. This natural cleavage renders it simple to hew the 20 coal in brick-shape blocks, the long sides of which are known as the face, and the short sides, whose fracture is the least regular, are called the ends. The sides cleave bright and smooth, but the planes of bedding are dull and sooty, because of a black and fibrous powder, to which the name of 25 mineral charcoal, and sometimes of mother-of-coal, has been given, and which lies between the planes of cleavage. Mixed with this loose substance may plainly be seen the remains of the stems and leaves of plants. Mother-ofcoal soils everything it touches, and renders the miners at 30 work, and even visitors at the workings, in a very short time as black as soot. It also ignites, instantly, in presence of a light, and some dreadful explosions in the pits, the cause of which could not be clearly traced, has been thought to be due to the firing of coal-dust.

A VISIT TO A COAL MINE

Like Columbus in America, visitors to the coal mines land themselves in a new world. The aspect of the district is quite strange. Everything is black. Coal in huge black mounds is everywhere. Grim, skeleton arms and wheels, 5 the tackle of the different pits, stretch out in the murky skies, hoisting and lowering the cages of coal, while dense black smoke from the furnace shafts and coking ovens obscure the sun and fill the air with flakes of soot.

Everything here is black. The scanty herbage which 10 wrestles with fate, and the few sheep which crop it, are

black. The railroad trucks and roads are black. Black barges laden with coal are towed along black paths through ink-black canals.

Let us now wend our way to a large mine near, directed 15 by lurid streams of natural gas, which are ever flaring, night and day, fed from the exhaustless stores of "bottled sunshine," as George Stephenson said, which the ancient ages placed to man's account in the deep crust of the earth. Careful scrutiny of our Davy lamps, to see them lighted 20 and locked, goes on while the gear of the pit moves; the stout wire band or rope starts on its downward course, swift as a dart, and its twin brother mounts upwards as fast, the one freighted with a cage of miners bound for the bottom, the other with a cage of coal for the top. We look 25 over into the dark depth. Whoever could have first thought of digging such a hole as this to see what he could find? We cannot stop to think. Our foot is on the plank, and we go "downstairs," dangling at the end of a quarter of a mile of rope.