the great coal-making epoch that was approaching, in stems and impressions of several of the genera of plants that were soon afterwards so multiplied.

Some years ago there were authors of weight who inclined to the opinion that coal had been formed by the drifting of large masses of vegetable matter into bays or estuaries, and they pointed to the "rafts" of the lower Mississippi as examples of a similar process still in action. But since due attention has been paid to the constant presence of the roots in the floor of the seams, to the upright trunks-often one series above another—and to the high state of preservation of the most delicate remains, it has been generally agreed that most of the appearances are explained by assuming that the vegetation grew on the spot where we now find it.* Some writers there are still who have a hankering after the old aquatic origin, and, supported by the evidence of fishes and marine shells, would assign salt water as a habitat for some of the coal plants. But with others the doubtful point is whether the trees and undergrowth flourished on dry land or swampy sea margins. We can no longer doubt that the under-clay was a true soil, in which the great Sigillaroid trees were fixed by their tap-roots, their spreading radical branches, and filamentous rootlets. How many generations of these trees may have risen to maturity and died away before the conditions were favourable to their being preserved, it is hard to surmise; but at length, when a mingled matting of vege

* Franz von Beroldingen appears to deserve the credit of first suggesting the view that the coal-beds are the peat-bogs of a former age, converted first into brown coal and afterwards into stone coal. (Beobachtungen, &c., die Mineralogie betreffend, 1778.) In this theory he was supported by De Luc, and after many years by Schlotheim, Nöggerath, and Lindley and Hutton.

table matter, stems, roots, leaves, &c., had accumulated, like the pulpy mass of a modern peat-bog, the surface of the area was, with much uniformity, depressed. Then would flow back the waters, fresh or salt, over their ancient domain, and, according to the sediment they were able to carry, would deposit sand or mud to be one day known as the rock-or the shale-roof. The Mollusca above enumerated then burrowed in the soft ooze, close upon the top of the buried vegetation; in many cases the stumps of the old forest remained standing, whilst mud or silt was deposited around them, until the central portion of the trunk would rot away, serve for a time as an asylum for some of the lizards or land-shells of the period, and then get filled in with petrifying matter. As the water deepened it was haunted by fish of many kinds, whose exuviæ fell to the bottom and were there buried up, and thus bed after bed of sediment accumulated, sometimes to the depth of a few feet, sometimes to hundreds of yards— if the continuous depression of the land was maintained -until circumstances favoured again the formation of a proper soil (the under-clay), and of a growth of trees and plants, when we should have a recurrence of the same phenomena.

An enormous bulk of vegetable matter would be needed thus to form one of our thicker seams of coals; but we have seen how the latter are generally divisible into several beds, and these again into thin laminæ, whilst we know that peat-bogs of the present day, without the special advantages of the coal jungle, attain depths of 30 or 40 feet. It has been estimated that eight feet thick of packed woody substance would be needed to make one foot of coal; but we may take it for granted that such an amount would represent only

a fraction of the total amount of vegetation that flourished at the time, since much of it must doubtless have escaped from the preservative process of interment.

We cannot afford space to dwell on the chemical argument by which this derivation of the different kinds of coal is shown to be probable; but the following table, borrowed from Dr. Percy's "Metallurgy," supplies at a glance an illustration of the successive steps in the change from woody tissue to anthracite. The porportions of carbon in each substance being taken at the constant amount of 100, the hydrogen and oxygen will be found to have been more and more eliminated.

When the buried forest had once been fairly covered up by hundreds, and as the land sank, by thousands of feet of rock, we may conceive it subjected to those conditions of pressure, temperature, and moisture, which were needed to change it into that condensed form of fuel now so necessary to mankind.

And when at length, after ages of due preparation, portions of the coal formation were upheaved into the islands and continents, the seams of coal were brought into a position to be accessible to man, and the forces of the sunbeams, which fell upon the jungles of the primeval world, are again unlocked and made subservient to our use, when we now decompose by burning those compounds which had been called into existence by the solar light and heat.

CHAPTER IV.

COALFIELDS OF THE NORTH.

In order to enable us to form a due estimate of the coal resources of the various countries, we must glance at the extent and character of the coal-measures as they are developed in the different districts; and since the history and commercial importance of the coalfield of Newcastle give it the pre-eminence, we may conveniently start from that focus of activity.

It must be premised that the limits of a coalfield are not to be confounded with the area coloured as "coal-measures" in a geological map; for although in some regions (as in South Wales) it is one and the same thing, the coal-seams are often well known and largely worked beneath other newer formations, which in a map are represented by their proper colour, whether they overlie coal-measures or any other older rocks. We shall, therefore, in many instances have to speak of a coalfield as such, where it signifies the extent of proved coal-producing ground, whatever the mere covering may be composed of.

On examination of a geological map it will be seen that, coming southward from the Durham coalfield on one side of the central chain of North English hill country, and from that of Cumberland on the other, a large interval separates them from those of Yorkshire and Lancashire respectively. It will be seen, too, that there are certain features of connection in each case between the East and the West, which it is not so easy to establish between North and South, and we may therefore take one division for this chapter as including the

coal regions north of a line drawn from the mouth of the Tees westward through Kendal and the south side of the Lake country.

About equidistant from the Irish Sea on the west and the North Sea on the east rises the broad backbone of the hill country, composed of the carboniferous, limestone with all its numerous subdivisions so carefully studied by the lead-miners of those breezy fells, and bearing on its culminating points, and on the high ground extending for many miles breadth on the east, a capping of millstone-grit. On the west side, or towards Penrith, this main chain has been greatly disturbed and abruptly broken at an early geological period, whilst on the other side the land slopes more uniformly from the high ground. The strata here, inclining gently eastward, partake of the same regularity, and as we proceed towards the coast, succeed in ever ascending order till the various coal-seams "put in," one after the other, and are at length similarly capped by the magnesian limestone, and soon afterwards-not cut off, but surmounted-by the sea. The field of the Blythe, Tyne, and Wear, so-called after its rivers, extends from the Coquet on the north to near the Tees on the south, for about 50 miles in length, with a breadth of about 20 miles for a great part of the way, till it narrows to a point when it passes north of the Blythe, an area in all of 705 miles. For some miles in breadth along the western side, only a few of the lower seams are worked; then, in a line ranging through Newcastle and Durham, we get the full number of the workable seams; and again, following a sinuous course from Tynemouth past Houghton-leSpring to near Bishop Auckland, the overlying