still seen imbedded in the fire-clay on which, as a soft muddy soil, they originally grew. It is probable, however, that, notwithstanding such elevations of the sea-bed, there was a general subsidence of the ground during the accumulation of these strata, for we see that the peaty morass, represented now by the coal-seam, ere long sank beneath the waters, with the inroads of which it was unable to keep pace, while there slowly silted over it a muddy sediment that hardened at length into what is now a seam of shale. But this order of things had been in existence for but a comparatively short period when the igneous forces broke out again, ejecting a stream, of molten lava that spread along the bottom of the shallow waters and hardened as before into a sheet of greenstone. This was followed by an abundant shower of dust and lapilli, along with numerous large masses of greenstone and basalt. These falling into the water accumulated on the upper surface of the lava-stream, then somewhat cooled, and formed in the end a stratum of ash of a rubbly conglomeritic aspect. That the sheet of greenstone really spread out along the sea-bottom before the ejection of the ash, and was not intruded among the beds at a later period,--that, in short, it must be regarded as a contemporaneous and not as an intrusive rock, seems sufficiently shown by its great regularity and evenness, and by the unaltered condition of the fine soft felspathic matter which covers its upper surface. It was assuredly in a highly-heated condition when poured out, as may be gathered from the baked aspect of the mud over which it rolled; but it had cooled and solidified, at least along its upper surface, ere buried beneath the shower of ashes. The last bed exhibited in the section is a grey sandstone, with many carbonaceous streaks and traces of land-plants, showing a pause in the volcanic activity of the district, during which the streams from the land brought down sandy sediment, with an abundant admixture of macerated leaves, branches, and other drift-wood. It thus appears that not only were the plains and hills of the Carboniferous era richly clothed with vegetation, and its waters crowded with animals, but that then, as now, subterranean forces were at work, sometimes elevating, sometimes depressing the area alike of the land and of the sea; while, not unfrequently, melted lava rose from below, rolling along the bottom of the waters, and showers of ashes were flung far and wide through the air, settling at last as a thickening sediment along the floor of the sea, or athwart the marshy swamps of the delta. Whether the interior of the land had burning cones among its pine-covered hills we know not yet. Such, however, probably existed; nay, there may have been among the higher peaks some "snowy pillar of heaven," like the Ætna of Pindar, raising its smoking summit among everlasting crags of ice in solitudes lifeless and bare.[77]