FORMATION OF BOGS. 29 
and of smaller animals, insects, and birds, in destroying the 
woods.* 
Bogs generally originate in the checking of watercourses by 
the falling of timber or of earth and rocks, or by artificial ob- 
structions across their channels. If the impediment is sufficient 
to retain a permanent accumulation of water behind it, the 
trees whose roots are overflowed soon perish, and then by their 
fall increase the obstruction, and, of course, occasion a still 
wider spread of the stagnating stream. This process goes on 
until the water finds a new outlet, at a higher level, not lable 
Peat beds have sometimes a thickness of ten or twelve yards, or even more. 
A depth of ten yards would give 48,000 cubic yards to the acre. The greatest 
quantity of firewood yielded by the forests of New England to the acre is 100 
cords solid measure, or 474 cubic yards; but this comprises only the trunks 
and larger branches. If we add the small branches and twigs, it is possible 
that 600 cubic yards might, in some cases, be cut on an acre. This is only 
one eightieth part of the quantity of peat sometimes found on the same area. 
It is true that a yardof peat and a yard of wood are not the equivalents of 
each other, but the fuel on an acre of deep peat is worth much more than 
that on an acre of the best woodland. Besides this, wood is perishable, and 
the quantity on an acre cannot be increased beyond the amount just stated ; 
peat is indestructible, and the beds are always growing. See post, Chap. IV. 
Cold favors the conversion of aquatic vegetables into peat. Asbjdrnsen says 
some of the best peat he has met with is from a bog which is frozen for forty 
weeks in the year. 
The Greeks and Romans were not acquainted with the employment of peat 
as fuel, but it appears from a curious passage which I have already cited from 
Pliny, WV. H., book xvi., chap. 1, that the inhabitants of the North Sea coast 
used what is called kneaded turf in his time. This is the finer and more 
thoroughly decomposed matter lying at the bottom of the peat, kneaded 
by the hands, formed into small blocks and dried. It is still prepared in pre- 
cisely the same way by the poorer inhabitants of those shores. 
But though the Low German tribes, including probably the Anglo-Saxons, 
have used peat as fuel from time immemorial, it appears not to have been 
known to the High Germans until arecent period. At least, Ican find neither 
in Old nor in Middle High German lexicons and glossaries any word signifying 
peat. Zurb indeed is found in Graff as an Old High German word, but only 
in the sense of grass-turf, or greensward. Peat bogs of vast extent occur in 
many Hich German localities, but the former abundance of wood in the same 
regions rendered the use of peat unnecessary. 
* Seo Chapter II., post. 
