Peat, a substance formed by the decomposition of plants amidst much moisture, as in marshes and morasses, and sometimes described as a kind of humus or soil, formed by the accumulation of the remains of mosses and other marsh-plants. The remains of the plants are often so well preserved in it that the species can be easily distinguished. Reeds, rushes, and other aquatic plants may usually be traced in peat, and stems of heath are often abundant in it; but it chiefly consists in the northern parts of the world of different species of Sphagnum or Bog-moss (see BOG-PLANTS). Mosses of this genus grow in very wet situations, and throw out new shoots in their upper parts whilst their lower parts are decaying and being converted into peat; so that shallow pools are gradually changed into bogs. Stools and trunks of trees often occur under peat in the British Islands and in north-western Europe generally. And not only so, but similar stools and trunks frequently are met with occupying a middle position in many peat-bogs—i.e. resting on peat and covered by a variable thickness of the same accumulation. It cannot be doubted that the overturning of trees, whether by natural causes or by man's hand, would in many cases impede surface drainage, and so eventually give rise to the formation of bogs. But there is reason to suspect that the succession of 'buried forests' and peat so frequently seen in the bogs of north-western Europe points to climatic changes (see POST-GLACIAL SYSTEM). Peat is vegetable matter more or less decomposed, and passes by insensible degrees into Lignite (q.v.). The less perfectly decomposed peat is generally of a brown colour; that which is more perfectly decomposed is often nearly black. Moist peat possesses a decided and powerful antiseptic property, which is attributed to the presence of gallic acid and tannin, and is manifested in the perfect preservation not only of ancient trees and of leaves, fruits, &c., but sometimes even of animal bodies. Thus, in some instances human bodies have been found perfectly preserved in peat after the lapse of centuries.
The formation of peat takes place only in the colder parts of the world. In warm regions the decay of vegetable substances after life has ceased is too rapid. The surface covered by peat is very extensive in all temperate regions. In England it is considerable; it is greater in Scotland, and very great in Ireland. Some large peat-bogs occur in the south of Europe, even near the sea, and in more northern regions the mosses or bogs are still more extensive; they occur also in the northern United States, but more extensively in Canada and Newfoundland. For their physical characters and the mode of reclaiming them, see BOG, and WASTE LANDS. Mere peat is not a good soil, even when sufficiently drained, but by the application of lime, marl, &c. it is soon converted into valuable land, yielding excellent crops. A mixture of peat is often of benefit to soils otherwise poor; and for many shrubs, as rhododendrons, kalmias, whortleberries, &c., no soil is so suitable as one largely composed of peat.
Peat is the ordinary fuel of great part of Ireland, and is still much in request in the hillier parts of Scotland and England. In Holland, Denmark, and parts of north Germany it is also in use for the same purpose. Peat is a light and bulky kind of fuel, and cannot be conveyed to considerable distances without too great expense. Efforts have, however, been made to render it more generally useful, and so to promote the reclaiming of bogs, by compressing it until its specific gravity is nearly equal to that of coal. For this purpose it is first reduced to a pulp. But the process has not yet been advantageously prosecuted on an extensive scale, though numerous machines for the purpose have been patented in Germany and in the United States. Peat-charcoal, made from uncompressed peat, is very light and inflammable, and therefore unsuitable for many purposes, but for others it is particularly adapted, and no kind of charcoal excels it in antiseptic and deodorising properties. Peat-charcoal is highly esteemed for the smelting of iron and for working and tempering the finer kinds of cutlery. Charcoal made from compressed peat is in density superior to wood-charcoal, and is capable of being used as coke. But the conversion of peat into charcoal has not proved remunerative; and the attempts to obtain valuable products (pyroligneous acid, ammonia, inflammable oils, burning gas, tar, &c.) from its destructive distillation have been similarly unsuccessful.
Peat, specially prepared, is very serviceable for horses' bedding, &c. As antiseptic, it has been used for laying on wounds. Flower-pots are sometimes made of peat; it is easy to transplant flowers growing in them without loosening the earth from the roots, the pot being readily cut to pieces; and liquid manure applied outside finds its way to the roots.
See Rennie, Essays on the Natural History and Origin of Peat-moss (1810); Aiton, Treatise on the Origin, Qualities, and Cultivation of Moss-earth (1811); Steele, Natural and Agricultural History of Peat-moss or Turf-bog (1826); a parliamentary Report on the Destructive Distillation of Peat (1851); Rev. J. Peter, The Peat Mosses of Buchan (1875); J. Geikie, Prehistoric Europe.