e plants and trees had been
swept down by rivers into the sea, as the sands and muds which buried
them had been. And it was known that at the mouths of certain
rivers--the Mississippi, for instance--vast rafts of dead floating
trees accumulated; and that the bottoms of the rivers were often full
of snags, etc.; trees which had grounded, and stuck in the mud; and
why should not the coal have been formed in the same way?

Because--and this was a serious objection--then surely the coal would
be impure--mixed up with mud and sand, till it was not worth burning.
Instead of which, the coal is usually pure vegetable, parted sharply
from the sandstone which lies on it. The only other explanation was,
that the coal vegetation had grown in the very places where it was
found. But that seemed too strange to be true, till that great
geologist, Sir W. Logan--who has since done such good work in Canada-
-showed that every bed of coal had a bed of clay under it, and that
that clay always contained fossils called Stigmaria. Then it came
out that the Stigmaria in the under clay had long filaments attached
to them, while when found in the sandstones or shales, they had lost
their filaments, and seemed more or less rolled--in fact, that the
natural place of the Stigmaria was in the under clay. Then Mr.
Binney discovered a tree--a Sigillaria, standing upright in the coal-
measures with its roots attached. Those roots penetrated into the
under clay of the coal; and those roots were Stigmarias. That seems
to have settled the question. The Sigillarias, at least, had grown
where they were found, and the clay beneath the coal-beds was the
original soil on which they had grown. Just so, if you will look at
any peat bog you will find it bottomed by clay, which clay is pierced
everywhere by the roots of the moss forming the peat, or of the
trees, birches, alders, poplars, and willows, which grow in the bog.
So the proof seemed complete, that the coal had been formed out of
vegetation growing where it was buried. If any further proof for
that theory was needed, it would be found in this fact, most
ingeniously suggested by Mr. Boyd Dawkins. The resinous spores, or
seeds of the Lepidodendra make up--as said above--a great part of the
bituminous coal. Now those spores are so light, that if the coal had
been laid down by water, they would have floated on it, and have been
carried away; and therefore the bit