VII] 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- 

 landa 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, 19006: 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. 



