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 (q.v.), 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 disting,uislisd. 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 (q.v.), or bog-moss. Mosses of this genss 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. It was at one time believed that bogs oared their origiu to the destruction of forests, the fallen trees impeding the natural drainage, and causing the growth of those marsh-plants of which peat is formed; and this theory was supported by reference to instances supposed to be authenticated by tradition—as that of the moor of Hatfield in Yorkshire, now consisting of about 12,000 acres of peat, and said to have been a forest of firs, till " the Romans under Ostorius, having slain many Britons, drove the rest into the forest," which was then destroyed by the victors. There are, however, satisfactory proofs that peat has accumulated in many places around trees; and firs remaining in their natural position have been found to have 0 or 7 ft. of peat under their roots, although other trees, as oaks, are commonly found with their stumps resting on the soil beneath the peat. Yet it is not improbable that the destruction of forests may, in some instances, by impeding the course of the streams which flowed through them; have caused the stagnation of water from which the growth of peat resulted. Some of the largest mosses and fens of Europe occupy the place of forests, which were destroyed by order of Severus and other Roman emperors; and some of the British forests, now mosses, as well as some of those of Ireland, were cut because they harbored wolves or outlaws. The overthrow of a forest by a storm in the 17th c. is known to have caused the forma tion of a peat-moss near loch Broom, in Ross-shire. Layers of trees are not unfrequently
found in peat, which seem to have been suddenly deposited in their horizontal position, and sometimes to have been felled by human hands. It is not improbable, however, that sometimes peat has been formed where the soil lies been exhausted by the long-con tinued growth of one kind of tree. The growth of peat is often rapid: hogs have been known to increase 2 in. in depth in a year. The surface of a bog sometimes becomes a floating mass of long interlaced fibers of plants, known in Ireland as Old Wires' Tim The vegetation on the surface is sometimes very green and compact, like a beautiful turf.
Peat is vegetable matter more or less decomposed, and plisses by insensible degrees into lignite (q.v.). The less-perfectly decomposed peat is generally of a brown color; 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 not only in the perfect preservation of ancient trees and of leaves, fruits, etc.-, 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 may be regarded as one of the most important geoloftical changes now in evident progress. It takes place, however, only in the colder parts of the world. In warm regions, the decay of vegetable substances, after life has ceased, is too rapid tp permit the formation of peat. The surface covered by peat is very extensive in all the colder parts of the world; although in the southern hemisphere no moss seems to enter into its composition; and the South American peat is said by Mr. Darwin to be formed of many plants, but chiefly of astelia pumila, a phanerogamous plant of the rush, family. The surface covered by peat even in England is considerable; it is greater in Scotland. and very great in Ireland. Extensive tracts are Covered with peat eveu in the southern countries of Europe, and sometimes even near the sea; and in more northern regions, the mosses or bogs are still more extensive. For their physical and the mode of reclaiming them, or converting them into arable land, see BOG.