m, had appeared upon the globe, there flourished a vegetation not
only remarkable for its luxuriance, but also for the circumstance that it
consisted to a preponderating extent of non-flowering or cryptogamic
plants. In swampy areas, such as the deltas at the mouths of great rivers,
or in shallow lagoons bordering a coast margin, the jungles of ferns and
tree-ferns, club-mosses and horse-tails, sedges, grasses, &c., grew and
died down year by year, forming a consolidated mass of vegetable matter
much in the same way that a peat bed or a mangrove swamp is accumulating
organic deposits at the present time. In the course of geological change
these beds of compressed vegetation became gradually depressed, so that
marine or fresh-water sediment was deposited over them, and then once more
the vegetation spread and flourished to furnish another accumulation of
vegetable matter, which in its turn became submerged and buried under
sediment, and so on in successive alternations of organic and sedimentary
deposits.

But these conditions of climate, and the distribution of land and water
favourable to the accumulation of large deposits of vegetable matter,
gradually gave way to a new order of things. The animals and plants
adapted to the particular conditions of existence described above gave
rise to descendants modified to meet the new conditions of life. Enormous
thicknesses of other deposits were laid down over the beds of vegetable
remains and their intercalated strata of clay, shale, sandstone, and
limestone. The chapter of the earth's history thus sealed up and stowed
away among her geological records relates to a period now known as the
Carboniferous, because of the prevalence of seams or beds of coal
throughout the formation at certain levels. By the slow process of
chemical decomposition without access of air, modified also by the
mechanical pressure of superincumbent formations, the vegetable deposits
accumulated in the manner described have, in the lapse of ages, become
transformed into the substance now familiar to us as coal.

Although coal is thus essentially a product of Carboniferous age, it must
not be concluded that this mineral is found in no other geological
formation. The conditions favourable for the deposition of beds of
vegetable matter have prevailed again and again, at various periods of
geological time and on different parts of the earth, although there is at
present no distinct evidence that such a luxur