30 EORMATIOlSr OF BOGS. 



is gradually converted from a pond to a quaking morass. The 

 morass is slowly soKdified 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 re-estabhshed.* 



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 drairi- 

 age, 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 haK-civilized regions, too, 

 wind-falls are more frequent than in those where the forest is 

 unbroken, because, when openings have been made in it for agri- 

 cultural 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 which would then have 

 fallen to the ground only one by one, as natural decay brought 

 them down.f Besides this, the flocks bred by man in the pas- 



*" 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 metres, 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 pauvres, 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 groimd for the oak. — Vaupell, Bogens Indvandring, pp. 39, 40. 



The growth of the peat not unfrequently raises the surface of bogs consid- 

 erably above the level of the surrounding country, and these sometimes burst 

 and overflow lower grounds with a torrent of mud and water as destructive aa 

 a current of lava. 



f Careful examination of the peat mosses in North Sjselland — which are sc 



