The accumulations of stagnant or stagnating water originating in bogs are distinguished into Trask, stagna, and Tjernar or Tjarnar (sing. Tjern or Tjarn), stagnatiles. Trask are pools fed by bogs, or water emanating from them, and their bottoms are slimy; Tjernar are small Trask situated within the limits of Mossar.--L.L. Laestadius, om Mojligheten af Uppodlingar i Lappmarken, pp. 23, 24. Although the quantity of bog land in New England is less than in many other regions of equal area, yet there is a considerable extent of this formation in some of the Northeastern States. Dana (Manual of Geology, p. 614) states that the quantity of peat in Massachusetts is estimated at 120,000,000 cords, or nearly 569,000,000 cubic yards, but he does not give either the area or the depth of the deposits. In any event, however, bogs cover but a small percentage of the territory in any of the Northern States, while it is said that one tenth of the whole surface of Ireland is composed of bogs, and there are still extensive tracts of undrained marsh in England. The amount of this formation in Great Britain is estimated at 6,000,000 acres, with an average depth of twelve feet, which would yield 21,600,000 tons of air-dried peat.--Asbjornsen, Tore og Torodrift, Christiania, 1868, p. 6. 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 yard of 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 of 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. Asbjornsen 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, N. 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 precisely the same way by the poorer inhabitants of those shores.