succession of forest trees--appear to have gone through this gradual
process of drying, and the birch, which grow freely in very wet soils,
has contributed very effectually by its annual deposits to raise the
surface above the water level, and thus to prepare the ground for the
oak.--Vaupell, Bogens Indvandring, pp. 39, 40.

The growth of the peat not unfrequently raises the surface of bogs
considerably above the level of the surrounding country, and they
sometimes burst and overflow lower grounds with a torrent of mud and
water as destructive as a current of lava.]

In countries somewhat further advanced in civilization than those
occupied by the North American Indians, as in mediaeval Ireland, the
formation of bogs may be commenced by the neglect of man to remove, from
the natural channels of superficial drainage, the tops and branches of
trees felled for the various purposes to which wood is applicable in his
rude industry; and, when the flow of the water is thus checked, nature
goes on with the processes I have already described. In such
half-civilized regions, too, windfalls are more frequent than in those
where the forest is unbroken, because, when openings have been made in
it for agricultural or other purposes, the entrance thus afforded to the
wind occasions the sudden overthrow of hundreds of trees which might
otherwise have stood for generations and have fallen to the ground, only
one by one, as natural decay brought them down. [Footnote: Careful
examination of the peat mosses in North Sjaelland--which are so abundant
in fossil wood that, within thirty years, they have yielded above a
million of trees--shows that the trees have generally fallen from age
and not from wind. They are found in depressions on the declivities of
which they grew, and they lie with the top lowest, always falling
towards the bottom of the valley.--Vaupell, Bogens Indvandring i de