50 
Dr MacCuliocli on Peat 
large submarine plains at considerable depths under the sea, and, 
by detaining the sand and mud, gradually raises the bottom so 
far above the liigh-water mark, as to enable it to afford a place 
for the plants of the preceding catalogue. By the bulk and 
extent of its roots, it also serves to form the principal part of 
the peat stratum which is found on sea-shores. 
The several varieties above enumerated, include all the de- 
positions of peat which are found in their natural situations 
but another variety remains, which was already mentioned, and 
which it is necessary to notice, before quitting this part of the 
subject. It consists of the finer parts of perfect peat, which 
have been transported by water to cavities capable of detaining 
them. This transported peat is rare in Scotland, and generally 
occupies small patches in mountainous land, where it produces 
a liquid or trembling bog : on the Continent of Europe, it ap- 
pears to form more extensive tracts, and to be of considerable 
importance. When drained, it constitutes one of the most solid 
and perfect varieties of peat. 
The progress of change from the living vegetable to peat, 
is most easily traced in the flat mosses of plains, and may be 
examined in the deep sections which are made for procuring 
fuel. In these, a regular gradation may be traced, from the 
spongy half-decomposed vegetable matter to the solid inorganic 
peat, in which nearly all traces of the plants have been obliterated. 
A similar gradation, but less perfect, may be found in moun- 
tain-peat ; but the progress of the other varieties is, from their 
peculiar nature, less susceptible of examination. Where the 
living plants terminate, their roots are found intermixed with 
the half-decomposed matter, produced by their leaves and frag- 
ments, forming a spongy mass. Lower down in the stratum, 
the pulverized peat is seen mixed with a few fibres or frag- 
ments still resisting decomposition. These gradually disappear 
in the progress downwards, until at length a finely powdered 
substance alone is found ; the process being completed to the eye 
in the total destruction of all the organized bodies. When this 
process has occurred on a drained declivity, the pure peat forms 
the powdery heath-soil used by gardeners for rearing certain 
plants ; where, on the contrary, the soil is wet or inundated, 
the powder is intermixed with water, which, on being drained. 
