ited upon the mud,
pressed it into shale, and the vegetable matter, still more reduced in
volume by this additional pressure, is prepared for its final conversion
into shale. In time the basin becomes shallow from the decomposition of
sediment on its bottom, and then we have another marsh with its myriad
plants; another accumulation of vegetable matter takes place, which by
similar processes is also buried. Where thirty or forty seams of coal
have been found one below another, we have evidence of land and water
thus changing places many times.

When vegetable matter is excluded from air and under great pressure, it
decomposes slowly, parting with carbonic acid gas; and is first changed
into lignite or brown coal, and then into bituminous coal, or the soft
coal that burns with smoke and flame. I have been in a coal-mine where
the carbonic acid gas, pouring from a crevice in the coal, put out a
lighted candle. The high temperature to which the coal has been
subjected when buried at great depths has also probably assisted in
producing this change; and where that temperature has been very high,
the coal by the influence of the heat having parted with its inflammable
gases, we have the hard or anthracite coal, which burns with little or
no flame and without smoke. It is indeed coal made into coke under
tremendous pressure, and this is the kind of coal which Americans use
exclusively in their dwelling-houses and monster hotels.

It was at first supposed that the plants of the carboniferous times were
bamboos, palms, and gigantic cactuses, such as are now found in tropical
regions, but a more careful examination of them shows that, with the
exception of the tree-fern now found in the tropics, they differ from
all existing trees. A large proportion of the plants of the
coal-measures were ferns, some authorities say one-half. From their
great abundance we may infer the great heat and moisture of the
atmosphere at the time when they grew, as similar ferns at the present
day are only found in the greatest abundance on small tropical islands
where the temperature is high. Coal often contains impressions of fern
leaves and palm-like ferns--no less than 934 kinds are drawn and
described by geologists. Many animals and insects are found in the coal,
such as large toad-like reptiles with beautiful teeth, small lizards,
water lizards, great fish with tremendous jaws, many insects of the
grasshopper tribe, but none of these are of the s