very thin layers, with a kind of black dust between them.

The next thing you will call to mind is that this coal burns and gives flame and heat, and that this means that in some way sunbeams are imprisoned in it ; lastly, this will lead you to think of plants, and how they work up the strength of the sunbeams into their leaves, and hide black carbon in even the purest and whitest substance they contain.

Is coal made of burnt plants, then } Not burnt ones, for if so it would not burn again ; but you may have read how the makers of charcoal take wood and bake it without letting it burn, and then it turns black and will afterwards make a very good fire ; and so you will see that it is probable that our pieoe of coal is made of plants which have been baked and altered, but which have still much sunbeam strength bottled up in them, which can be set free as they burn.

If you will take an imaginary journey with me to a coal-pit near Newcastle, which I visited many years ago, you will see that we have very good evidence that coal is made of plants, for in all coal-mines we find remains of them at every step we take.

Let us imagine that we have put on old clothes which will not spoil, and have stepped into the iron basket (see Fig. 46) called by the miners a cage^ and are being let down the shaft to the gallery where the miners are at work. Most of them will probably be in the gallery ^, because a great deal of the coal in a has been already taken out. But we will stop in a because there we can see a great deal of the roof and the floor. When we land on the floor of the gallery we shall find ourselves in a kind of tunnel with railway lines laid along it and trucks laden with coal coming

Imaginary section of a coal-mine.

towards the cage to be drawn up, while empty ones are running back to be loaded where the miners are at work. Taking lamps in our hands and keeping out of the way of the trucks, we will first throw the light on the roof, which is made of shale or hardened clay. We shall not have gone many yards before we see impressions of plants in the shale, like those in this specimen (Fig. 47), which was taken out of a coal-mine at Neath in Glamorganshire, a few days ago, and sent up for this lecture. You will recognize at once the marks offerns (a), for they look like those you gather in the hedges of an ordinary country lane, and that long striped branch {U) does not look unlike a reed, and indeed it is something of this kind, as we

shall see by-and-by. You will find plenty of these impressions of plants as you go along the gallery and look up at the roof, and with them there will be others

Fig. 47.

A piece of shale with impressions of ferns and Calamite stems.

with spotted stems, or with stems having a curious diamond pattern upon them, and many ferns of various kinds.

Next look down at your feet and examine the floor.

Fig, 48.

Gtigmaria-^root or underground stem of Sigillaria. You will not have to search long before you will almost certainly find a piece of stone like that represented in Fig. 48, which has also come from Neath

Colliery.* This fossil, which is the cast of a piece of a plant, puzzled those who found it for a very long time. At last, however, Mr. Binney found the specimen growing to the bottom of the trunk of one of the fossil trees with spotted stems, called Sigillaria ; and so proved that this curious pitted stone is a piece of fossil root, or rather underground stem, like that which we found in the primrose, and that the little pits or dents in it are scars where the rootlets once were given off.

Whole masses of these root-stems, with ribbon-like roots lying scattered near them, are found buried in the layer of clay called the underclay which makes the floor of the coal, and they prove to us that this underclay must have been once the ground in which the roots of the coal-plants grew. You will feel still more sure of this when you find that there is not only one straight gallery of coal, but that galleries branch out right and left, and that everywhere you find the coal lying like a sandwich between the floor and the roof, showing that quite a large piece of country must be covered by these remains of plants all rooted in the underclay.

But how about the coal itself } It seems likely, when we find roots below and leaves and stems above, that the middle is made of plants, but can we prove it } We shall see presently that it has been so crushed and altered by being buried deep in the ground that the traces of leaves have almost been

1 am much indebted to Mr. John Willictms, of Neath, for procuring these lossils for me ; and also to Professor Judd for lending me gome for an eailier lecture.

destroyed, though people who are used to examhiing with the microscope, can see the crushed remains oi plants in thin slices of coal.

But fortunately for us, perfect pieces of plants have been preserved even in the coal-bed itself. Do you remember our learning in Lecture IV. that water with lime in it petrifies things, that is, leaves carbonate of lime to fill up grain by grain the fibres of an animal or plant as the living matter decays, and so keeps an exact representation of the object 1

Now, it so happens that in a coal-bed at South Ouram, near Halifax, as well as in some other places, carbonate of lime trickled in before the plants were turned into coal, and made some round nodules in the plant-bed, which look like cannon-balls. Afterwards, when all the rest of the bed was turned into coal, these round balls remained crystallized, and by cutting thin transparent slices across the nodule we can distinctly see the leaves and stems and curious little round bodies which make up the coal. Several such sections may be seen at the British Museum, and when we compare these fragments of plants with those which we find above and below the coal-bed, we find that they agree, thus proving that coal is made of plants, and of those plants whose roots grew in the clay floor, while their heads reached up far above where the root now is.

The next question is, what kind of plants were these Have we anything like them living in the world now } You might perhaps think that it would be impossible to decide this question from mere petrified pieces of plants. But many men have spent their whole Hves in deciphering all the fragments that could be found, and though the section given in Fig. 49 may look to you quite incomprehensible, yet

Contents of a coal-ball. (Carruthers.)

5", Stem of Sigillaria cut across. Z, Stem of Lepidodendron cut across. Z', Stem of Lepidodendron cut lengthways. /, cone of Lepidodendron (Lepidostrobus) cut across. Stem of Calamite cut across, Fruit of Calamite lengthways and across, Stem of a fern with fragments of fern-leaves scattered round it. The small round dots scattered here and there are the larger spores which have fallen out of the fruit-cones. a botanist can read it as we read a book. For example, at S and L, where stems are cut across, he can

• I am much indebted to Mr. Carruthers, of the British Museum, for allowing me to copy this figure from his original diagram of a coal-ball, and also for jiving me much valuable assistance.

learn exactly how they were built up inside, and compare theni with the stems of living plants, while the fruits cc and the little round spores lying near them, tell him their history as well as if he had gathered them from the tree. In this way we have learnt to know very fairly what the plants of the coal were like, and you will be surprised when I tell you that the huge trees of the coal-forests, of which we sometimes find trunks in the coal-mines from ten to fifty feet long, are only represented on the earth now by small insignificant plants, scarcely ever more than two feet, and often not many inches high.

Have you ever seen the little club- moss or Lycopodium which grows all over England, but chiefly in the north, on heaths and mountains } At the end of each of its branches it bears a cone made of scaly leaves ; and fixed to the Selaginella selaginoides. inside of each of these Species of club- moss bearing two leaves is a case called kinds of spores. a sporangium, full of little spores or moss-seeds, as we may call them, though they are not exactly like true seeds. In one of these club-mosses called Selagmella, the cases B near the bottom of the cone contain large spores while those near the top, A, contain a

powdery dust a. These spores are full of resin, and they are collected on the Continent for making artificial lightning in the theatres, because they flare when lighted.

Now this little Selaginella is of all living plants the one most like some of the gigantic trees of the coalforests. If you look at this picture of a coal-forest (Fig. si), you will find it difficult perhaps to believe that those great trees, with diamond markings all up the trunk, hanging over from the right to the left of the picture, and covering all the top with their boughs, could be in any way relations of the little Selaginella yet we find branches of them in the beds above the coal, bearing cones larger but just like Selaginella cones ; and what is most curious, the spores in these cones are of exactly the same kind and not any larger than those of the club-moss.

These trees are called by botanists Lepidodendrons, or scaly trees ; there are numbers of them in all coalmines, and one trunk has been found 49 feet long. Their branches were divided in a curious forked manner and bore cones at the ends. The spores which fell from these cones are found flattened in the coal, and they may be seen scattered about in the coal-ball (Fig. 49).

Another famous tree which grew in the coal-forests was the one whose roots we found in the floor or undei'clay of the coal. It has been called Sigillaria, because it has marks like seals {sigilhtm, a seal) all up the trunk, due to the scars left by the leaves when they fell from the tree. You will see the Sigillarias on the left-hand side of the coal-forest picture, having those curious tufts of leaves springing out of them at I A Forest of the Coal Period. Toface p. 180.

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