The whole place is so still, gloomy, and desolate,
that it goes by the name of the “Great Dismal
Swamp,” and you see we have here what might
well be the beginning of a bed of coal; for we know
that peat when dried becomes firm and makes an excellent
fire, and that if it were pressed till it was hard
and solid it would not be unlike coal. If, then,
we can explain how this peaty bed has been kept pure
from earth, we shall be able to understand how a coal-bed
may have been formed, even though the plants and trees
which grow in this swamp are different from those which
grew in the coal-forests.
The explanation is not difficult; streams flow constantly,
or rather ooze into the Great Dismal Swamp from the
land that lies to the west, but instead of bringing
mud in with them as rivers bring to the sea, they
bring only clear, pure water, because, as they filter
for miles through the dense jungle of reeds, ferns,
and shrubs which grow round the marsh, all the earth
is sifted out and left behind. In this way the
spongy mass of dead plants remains free from earthy
grains, while the water and the shade of the thick
forest of trees prevent the leaves, stems, etc.,
from being decomposed by the air and sun. And
so year after year as the plants die they leave their
remains for other plants to take root in, and the
peaty mass grows thicker and thicker, while tall cedar
trees and evergreens live and die in these vast, swampy
forests, and being in loose ground are easily blown
down by the wind, and leave their trunks to be covered
up by the growing moss and weeds.
Now we know that there were plenty of ferns and of
large Calamites growing thickly together in the coal-forests,
for we find their remains everywhere in the clay,
so we can easily picture to ourselves how the dense
jungle formed by these plants would fringe the coal-swamp,
as the present plants do the Great Dismal Swamp, and
would keep out all earthy matter, so that year after
year the plants would die and form a thick bed of peat,
afterwards to become coal.
Week 24
The next thing we have to account for is the bed of
shale or hardened clay covering over the coal.
Now we know that from time to time land has gone
slowly up and down on our globe so as in some places
to carry the dry ground under the sea, and in others
to raise the sea-bed above the water. Let us
suppose, then, that the great Dismal Swamp was gradually
to sink down so that the sea washed over it and killed
the reeds and shrubs. Then the streams from
the west would not be sifted any longer but would bring
down mud, and leave it, as in the delta of the Nile
or Mississippi, to make a layer over the dead plants.
You will easily understand that this mud would have
many pieces of dead trees and plants in it, which
were stifled and died as it covered them over; and
thus the remains would be preserved like those which
we find now in the roof of the coal-galleries.
