COAL.-PART II.

THERE are many other plants that enter into the composition of coal, but those I have mentioned are the four principal kinds. And it is not a little strange that we owe our coal to plants so low in the scale of nature, instead of to the lordly oaks and the princely palms. God shows us in this the value and importance of humble things-and proves to us that He is greatest even in His least productions.

The ancient coal forests composed of these trees must have looked very dark and sombre. The colour of the whole was one dull green, without the many delicate shades which we see in our woods. And all the year round there was no change of hue any more than in a pine-wood. The stillness of these old forests was awful; only the grand sound of the wind among the tops of the trees seemed at intervals like the distant roar of the sea. Animal life was scarce. Only huge reptiles, frogs, serpents, and crocodiles, glided silently in and out among the fern clumps, devouring each other.

Had man lived among these woods, he would have been sorely pinched for food and fuel, and implements of work. He could not have cultivated the trees for their fruit, or their blossoms, or their shade; their wood was too soft and spongy to have formed his furniture or his instruments, and it was too wet and pithy to serve even for fuel. The only form in which they could have been made useful was in making coal; and accordingly it is in this form alone that the great Creator has preserved them to us.

What the climate of the globe was at the time that

the coal-plants grew may be found out from the fact that ferns and club-mosses thrive best at the present day in moist sheltered islands. Some think that the presence of tree-ferns shows a tropical warmth; but in New Zealand, where they still occur, the climate is very much like our own: besides, tree-ferns are found even at a height of upwards of a thousand feet, beside the end of glaciers, waving their green feathery fronds over the never-melting ice. Ferns and club-mosses can therefore endure a wide range of temperature, so that their occurrence is no proof of a particular climate. In all probability, however, the climate of the coal period was warmer, moister, and more uniform than now obtains; and the huge size of the coal-plants, and the vast quantity of coal which they formed, seem to prove that the atmosphere was highly charged with that carbonic acid gas which plants take in and work into all their structures. The sameness of the climate is shown by the general character of the coal-plants being the same over every portion of the earth's surface, the same kinds being found in the most distant countries.

How coal was formed from these plants it is very difficult indeed to tell, because there is no process precisely of the same nature now going on anywhere. Most men of science believe that the plants have been swept down from the places where they grew by rivers or currents, and left in basins and firths of the sea or in fresh-water lakes. Sand and mud were heaped in alternate layers over them there, and thus formed the different strata of coal and sandstone which we now find in a coal-basin.

We can trace the gradual change between perfect wood and perfect coal in such situations, from the

blackened tree-trunks of our peat-bogs, through the lignites or brown coal, up through bituminous coal to the true coals which we burn in our grates. After a long interment of the heaped-up plants beneath the water, gradually undergoing there the chemical changes necessary to convert them into mineral condition, subterranean fires at last elevated the beds of coal above the waters, nearer the surface of the earth. Were it not for this the coal would have been buried far beyond the reach of man. Molten matter ran through the coal-basin in different directions, like the lava that flows down the sides of Vesuvius, and this hardened into what are called trap-rocks. By these fiery eruptions of trap the seams of coal were broken up and divided into parts that are easily worked, and the coal itself was brought from the profound depths within reach of

man.

We find many wonderful proofs of God's wisdom and care for man in thus preparing and arranging the coalbeds. Had they been formed on the surface, exposed to the air, they would have crumbled away into dross. But the precious treasure was safely hid deep down in the earth under beds of rocks, and yet not so deep as to be beyond the industry of man to get it by digging. It was not covered with hard rocks like granite and quartz, which would be very difficult to blast and penetrate; but with limestone, sandstone, shale, and clay ironstone, which can be easily pierced, and yet afford a sufficiently safe roof for the mine, and which are very valuable in themselves for man's uses.

A lump of coal, it is often said, is made up of sunbeams. We could believe this more readily of the diamond, which is just a crystal of coal, for it is so

bright and sparkling, and makes brilliant sunshine in a shady place. But even the dull black coal has been formed of the sunshine of long-forgotten summers. Every sunbeam that fell upon the club-mosses and ferns of the old coal forests, enabled them to withdraw the minute unseen carbon from the air, and form out of it their own solid tissue. They thus caged and imprisoned the floating light itself, and wrought its bright threads in their loom into the beautiful patterns of stem and leaf which they showed.

To form one of the little rings of wood in the trunk of one of the old pines took the sunshine of a long summer falling upon all its thousand leaves; and who can tell how much sunshine has been worked up in all the stores of coal that lie concealed under our feet? This prisoned sunshine we set free whenever we kindle a fire of coals. When the sun ceases to shine upon us in these cold misty wintry days, we draw upon the sunshine of a million years ago to drive away the frost and make us comfortable. The source of all labour is the sun; and we get the benefit of his labour when we burn the coal or the wood in which he has condensed and preserved it.

No ray of sunlight has ever been wasted or thrown

away.

It is because Nature has been so thrifty in her household ways that we are enabled to be so prodigal of our resources to-day, spending upwards of one hundred millions of tons of coal every year, and with that vast consumption of sun-labour producing all the varied and extraordinary work that we do under the

sun.

Why is a lump of coal black if it is composed of