word that designates its immaturity compared with anthracite.

Coal formed in the Triassic Period is found in a basin near Richmond,
Virginia. There is an abundance of this coal, but it has been subjected
to mountain-making pressure and heat, and is extremely inflammable. The
miners are in constant danger on account of coal gas, which becomes
explosive when the air of the shaft reaches and mingles with it. This
the miner calls "fire damp." North Carolina has coal of the same
formation, that is also dangerous to mine, and very awkward to reach, on
account of the crumpling of the strata.

There are beds of coal so pure that very little ash remains after the
burning. Five per cent, of ash may be reasonably expected in pure coal,
unmixed with sedimentary deposits. Such coal was formed in that part of
the swamp which was not stirred by the inflow of a river. Wherever muddy
water flowed in among the fallen stems of plants, or sand drifted over
the accumulated peat, these deposits remained, to appear later and
bother those who attempt to burn the coal.

[Illustration: Eocene fish]

[Illustration: _By permission of the American Museum of Natural History_

Trilobite from the Niagara limestone, Upper Silurian, of Western New
York]

[Illustration: Sigillaria, Stigmaria and Lepidodendron]

[Illustration: _By permission of the American Museum of Natural History_

Coal fern]

You know pure coal, that burns with great heat and leaves but little
ashes. You know also the other kind, that ignites with difficulty, burns
with little flame, gives out little heat, and dying leaves the furnace
full of ashes. You are trying to burn ancient mud that has but a small
proportion of coal mixed with it. The miners know good coal from poor,
and so do the coal dealers. It is not profitable to mine the impure part
of the vein. It costs as much to mine and ship as the best quality, and
it brings a much lower price.

The deeper beds of coal are better than those formed in comparatively
recent time and found lying nearer the surface. In many bogs a layer of
embedded root fibres, called peat, is cut into bricks and dried for
burning. Deeper than peat-beds lie the _lignites_, which are old beds of
peat, on the way to become coal. _Soft coal_ is older than lignite. It
contains thirty to fifty per cent. of volatile matter, and burns
readily, with a bright blaze. The richest of this bituminous coal is
called _fat_, or _fusing coal_. The bitumen ooz