Dr MacCulloch on Peat. 
51 
leaves it in a state often highly compacted and firm, producing 
that peat which is more valuable for the purposes of burning. 
A variety of modifications result from collateral circumstances 
or intermediate conditions ; the chief of which are, differences ^ 
in the nature of the vegetables, in the time during which the 
process has lasted, in the degree of drainage, and its occasional 
variations, and in the elevation, or other causes, affecting the 
temperature, or the moisture of the atmosphere. 
The commencement of the process is easily traced in the 
Sphagnum palustre^ which, in some situations, forms an import- 
ant ingredient in peat. In this plant, as the lower extremity 
dies and is decomposed, the upper, like many other mosses, 
sends forth fresh roots, and extends its offsets ; the individual 
becoming thus in a manner immortal, and supplying a perpe- 
tual fund of decomposing vegetable matter. A similar process, 
although less distinct, takes place in many of the rushes and 
grasses, the ancient roots and leaves dying, while the existence 
of the plant is perpetuated by the annual renovation of both. 
Many other vegetables add to the common stock, by their an- 
nual death, their existence being repeated in seedling plants; 
while others, of a perennial nature, contribute only by the or- 
dinary decay and renewal of their leaves. 
It is therefore evident, that the growth of peat is constant, 
but that it depends, at the same time, on the continuous growth 
of the vegetable covering. Hence mountain-peat is always in- 
creasing while it continues to bear those plants from which it 
was originally produced ; as its state of drainage, and looseness 
of texture, are such as never to refuse a hold to fresh plants of 
the same nature, even after the vegetating covering has been 
completely removed. There are certain cases, however, in which 
the growth of mountain-peat ceases, the vegetating covering be- 
ing replaced by plants which, under the circumstances that first 
produced them, continue to grow, and possess no tendency to 
form that substance. These cases are interesting to the agri- 
culturist, as they form, in fact, the several processes by which 
this species of peat is converted into green pasture or into arable ' 
land. The pasturage of sheep, the application of calcareous 
manures, or of clay or sand, burning, and the turning of the 
surface by agricultural implements, are the chief means by 
D 2 
