1 84 THE FAIRY-LAND OF SCIENCE. 
which lie in it ; and so soft, that everything would 
sink into it, if it were not for the matted roots of the 
mosses, ferns, and other plants which bind it together. 
You may dig down for ten or fifteen feet, and find 
nothing but peat made of the remains of plants 
which have lived and died there in succession for 
ages and ages, while the black trunks of the faljen 
trees lie here and there, gradually being covered up 
by the dead plants. 
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, 
