In Lancashire, busy
Lancashire, the same thing was happening, and even in the middle
of Yorkshire and Derbyshire the sea must have come up and washed
a silent shore where a vast forest spread out over at least 700
or 800 square miles. In Stafford-shire, too, which is now almost
the middle of England, another small coal-field tells the same
story, while in South Wales the deep coal-mines and number of
coal-seams remind us how for centuries and centuries forests must
have flourished and have disappeared over and over again under
the sand of the sea.
But what is it that has changed these beds of dead plants into
hard, stony coal? In the first place you must remember they have
been pressed down under an enormous weight of rocks above them.
We can learn something about this even from our common lead
pencils. At one time the graphite or pure carbon, of which the
blacklead (as we wrongly call it) of our pencils is made, was dug
solid out of the earth. but so much has now been used that they
are obliged to collect the graphite dust, and press it under a
heavy weight, and this makes such solid pieces that they can cut
them into leads for ordinary cedar pencils.
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