subaqueous
accumulation, since the same thing occurs in the case of modern submarine
forests. For these and other reasons, some of which are more fully stated
in the papers already referred to, while I admit that the areas of coal
accumulation were frequently submerged, I must maintain that the true
coal is a subaerial accumulation by vegetable growth on soils, wet and
swampy it is true, but not submerged."

I am almost disposed to doubt whether it is necessary to make the
concession of "wet and swampy"; otherwise, there is nothing that I know
of to be said against this excellent conspectus of the reasons for
believing in the subaerial origin of coal.

But the coal accumulated upon the area covered by one of the great
forests of the carboniferous epoch would in course of time, have been
wasted away by the small, but constant, wear and tear of rain and streams
had the land which supported it remained at the same level, or been
gradually raised to a greater elevation. And, no doubt, as much coal as
now exists has been destroyed, after its formation, in this way. What are
now known as coal districts owe their importance to the fact that they
were areas of slow depression, during a greater or less portion of the
carboniferous epoch; and that, in virtue of this circumstance, Mother
Earth was enabled to cover up her vegetable treasures, and preserve them
from destruction.

Wherever a coal-field now exists, there must formerly have been free
access for a great river, or for a shallow sea, bearing sediment in the
shape of sand and mud. When the coal-forest area became slowly depressed,
the waters must have spread over it, and have deposited their burden upon
the surface of the bed of coal, in the form of layers, which are now
converted into shale, or sandstone. Then followed a period of rest, in
which the superincumbent shallow waters became completely filled up, and
finally replaced, by fine mud, which settled down into a new under-clay,
and furnished the soil for a fresh forest growth. This flourished, and
heaped up its spores and wood into coal, until the stage of slow
depression recommenced. And, in some localities, as I have mentioned, the
process was repeated until the first of the alternating beds had sunk to
near three miles below its original level at the surface of the earth.

In reflecting on the statement, thus briefly made, of the main facts
connected with the origin of the coal formed during the carboniferous