And more, it is a provable
fact that only a portion of the coal measures is left. A great part
of Ireland must once have been covered with coal, which is now
destroyed. Indeed, it is likely that the coal now known of in Europe
and America is but a remnant of what has existed there in former
ages, and has been eaten away by the inroads of the sea.
Now whence did all that enormous mass of vegetable soil come? Off
some neighbouring land, was the first and most natural answer. It
was a rational one. It proceeded from the known to the unknown. It
was clear that these plants had grown on land; for they were land-
plants. It was clear that there must have been land close by, for
between the beds of coal, as you all know, the rock is principally
coarse sandstone, which could only have been laid down (as I have
explained to you already) in very shallow water.
It was natural, then, to suppose that these 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.
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