vil] MOORLAND ASSOCIATIONS 165 
ascent of the grassy hill sides north-west of Edale railway 
station, where the transition occurs at an altitude of about 
1500 feet (457 m.). The transitional area is usually characterized 
by much bilberry and crowberry. On the other hand, in following 
the course of an upland stream to its source, the moorland 
plateau is reached very gradually ; and, at the head of the valley, 
where a number of very different plant associations converge, 
a confused mixture occurs of siliceous pasture, scrub, and moor- 
land—a mixture which defies accurate cartographical represen- 
tation of the vegetation except on maps of a large scale. In 
descending a moorland plateau along the watershed between 
two lateral valleys, the moorland vegetation usually comes down 
to about 1000 feet (305 m.), and, in a few cases, as at Tintwistle 
Moor, near Glossop, to about 750 feet (229 m.). 
The rocky, exposed summits of the higher hills (figure 25) 
are characterized by the dominance of the bilberry (Vaccinium 
Myrtillus). Such bilberry moors are not of great extent; but 
they are interesting as linking the vegetation of the Pennines 
with that of central Scotland, where bilberry moors at high 
altitudes are widespread (R. Smith, 190006: 461—2). 
Sometimes the various moorland associations are sharply 
marked off from each other. Such sharply defined boundaries 
nearly always correspond with well-marked physiographical 
features. For example, a cotton-grass moor occupying a high 
plateau sometimes ceases quite sharply at an escarpment, on the 
plateau below which a heather moor may occur. The rocky 
escarpments, like the exposed rocky summits, are characterised 
by much bilberry; but the flora of the bilberry edges is richer 
than that of the bilberry ridges. Sometimes, however, the 
various moorland associations pass into each other very gradually, 
as when a heather moor adjoins a cotton-grass moor and there 
is not intervening escarpment. In such cases the transitional 
region is broad, and is marked by the co-dominance of the 
heather and the cotton-grass. On the accompanying vegeta- 
tion maps, such transitional areas are indicated by stippling the 
colour used for heather moors on the colour used for cotton- 
grass moors. 
