30 FORMATION OF BOGS. 
to similar interruption. The fallen trees not completely cov- 
ered by water are soon overgrown with mosses; aquatic and 
semiaquatic plants propagate themselves, and spread until they 
more or less completely fill up the space occupied by the waters 
and the surface is gradually converted from a pond to a 
quaking morass. The morass is slowly solidified by vegetable 
production and deposit, then very often restored to the forest 
condition by the growth of black ashes, cedars, or, in southern 
latitudes, cypresses, and other trees suited to such a soil, and 
thus the interrupted harmony of nature is at last reéstab- 
lished.* 
In countries somewhat further advanced in civilization than 
those occupied by the North American Indians, as in medizyval 
Ireland, the formation of bogs may be commenced by the neg- 
lect of man to remove, from the natural channels of superti- 
cial drainage, the tops and branches of trees felled for the 
various purposes to which wood is applicable in his rude indus- 
try; and, when the flow of the water is thus checked, nature 
goes on with the processes I have already described. In such 
* *¢ Aquatic plants have a utility in raising the level of marshy grounds, 
which renders them very valuable, and may well be called a geological func- 
tion. * * ¢ * 
‘‘ The engineer drains ponds at a great expense by lowering the surface of 
the water; nature attains the same end, gratuitously, by raising the level of 
the soil without depressing that of the water; but she proceeds more slowly. 
There are, in the Landes, marshes where this natural filling has a thickness of 
four métres, and some of them, at first lower than the sea, have been thus 
raised and drained so as to grow summer crops, such, for example, as maize.” 
—BoitEL, Mise en valeur des Terres pauores, p. 227. 
The bogs of Denmark—the examination of which by Steenstrup and Vaupell 
has presented such curious results with respect to the natural succession of 
forest trees—appear to have gone through this gradual process of drying, and 
the birch, which grows freely in very wet soils, has contributed very effectu- 
ally by its annual deposits to raise the surface above the water level, and thus 
to prepare the ground for the oak.—VAUPELL, Bigens Indvandring, pp. 89, 40. 
The growth of the peat not unfrequently raises the surface of bogs consid- 
erably 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, 
