PLANTING OF WATER CATCHMENT AREAS 109 
The moorland zone, occurring on the hills and mountains 
above the limits of the hill pasture, owes the peculiar 
character of its vegetation to the presence of peat, which 
varies in depth from a few inches to many feet, and overlies 
shale, sandstone, granite, and other rocks, but is rare on 
limestone. The peat also varies much in the quantity of 
water which it contains, and to this is due the various types 
of vegetation that are met with in the moorland zone. 
Botanists distinguish in this zone, as main types or associa- 
tions, heather moor, cotton-grass moor, Scirpus or spike-rush 
moor, bilberry moor, and Sphagnum moor. 
Heather grows on peat where the drainage is good, and 
is most vigorous when the water content of the peat is less 
than 50 per cent. It thus occupies the slopes of the hills 
and mountains immediately above the hill pasture, and 
ceases to thrive on the higher parts, where the ground is 
flatter and the drainage is impeded. There are thus, as a rule, 
extensive heather moors on the slopes with shallow and 
dry peat, succeeded above by cotton-grass, Scirpus, and 
Sphagnum moors, where the peat is deep and sodden with 
moisture. 
The lower limit of the heather moor is determined by 
the cessation of the peat and is very variable. It oecasion- 
ally descends in the Southern Pennines to 750 feet, but as 
a rule in this range seldom goes lower than 1000 feet 
elevation. Its upper limit is mainly a question of drainage 
and scarcely depends on altitude, as heather grows to a high 
elevation if the peat is dry. In the Southern Pennines the 
heather moor ascends to about 1500 feet, but it often gets 
up to 2000 feet in the Northern Pennines. The heather 
moors are the typical grouse moors, and are often preserved 
for shooting, the heather being set fire to every few years to 
promote young growth. 
The heaths in the south of England, which are often 
immense tracts at a low elevation, are also covered with 
heather, but are distinct from the heather moors in the 
nature of the soil. The soil of the moors is always peat, 
whereas that of the heaths is poor sand or gravel, the upper 
