Mosses and Peat 
and there deep pools of liquid black mud at least four 
feet deep, into which one’s foot is apt to slip. On the 
top of the hillocks the drying influence of the wind 
or of sunshine in a dry summer, hampers the growth 
of the Sphagnum, and perhaps a few plants of Poly- 
trichum or an adventurous heather seedling succeed 
in establishing themselves. Now begins a struggle 
for water between the Sphagnum and the heather 
roots, 
Should strong winds and a dry summer or two 
favour the growth of the latter, the roots will colonise 
the summit of the Sphagnum hillock and proceed to 
gradually kill out the moss all round them. The 
upper surfaces of all the hillocks may in that case 
become dry crumbly peat occupied by heather and 
masses of grey and white lichens with perhaps a few 
other plants. These heather plants are, however, separ- 
ated by an irregular network of living moss, deep mud 
holes, or possibly irregular water-courses full of various 
sedges and marsh plants. 
If the conditions are favourable, the whole surface 
of the moss will become dry dead peat, in which the 
heather, blaeberries, oxycoccus, &c., are growing vigor- 
ously, As soon as that happens, if sheep and cattle 
are excluded, seedling Scotch firs and birches begin to 
overgrow the moss, and quite a forest might develop 
Uf the neighbouring villagers would leave it alone. 
Such a Scotch fir forest was actually formed over 
most of the Scottish uplands (see p. 225). 
But it is not always the heather that wins the day ; 
should the outlet of the little streams which leave the 
moss be choked up, then the Sphagnum of a hillock 
would gradually grow up over the heather stems and 
suffocate it. 
On flat places, as, ¢g., where peat has been cut and 
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