You will feel still more sure
of this when you find that there is not only one straight gallery
of coal, but that galleries branch out right and left, and that
everywhere you find the coal lying like a sandwich between the
floor and the roof, showing that quite a large piece of country
must be covered by these remains of plants all rooted in the
underclay.
But how about the coal itself? It seems likely, when we find
roots below and leaves and stems above, that the middle is made
of plants, but can we prove it? We shall see presently that it
has been so crushed and altered by being buried deep in the
ground that the traces of leaves have almost been destroyed,
though people who are used to examining with the microscope, can
see the crushed remains of plants in thin slices of coal.
But fortunately for us, perfect pieces of plants have been
preserved even in the coal-bed itself. Do you remember our
learning in Lecture IV, that water with lime in it petrifies
things, that is, leaves carbonate of lime to fill up grain by
grain the fibres of an animal or plant as the living matter
decays, and so keeps an exact representation of the object?
Now, it so happens that in a coal-bed at South Ouram, near
Halifax, as well as in some other places, carbonate of lime
trickled in before the plants were turned into coal, and made
some round nodules in the plant-bed, which look like cannon-
balls.
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