164 VEGETATION OF THE PEAK DISTRICT [CH. 



and usually dominated by heather (figures 33 and 34 6): the peat 

 of the higher plateaux is much deeper and usually dominated 

 by the cotton-grass (figure 33 c). This typical regularity of the 

 moorland plateaux is, however, frequently broken by alternating 

 outcrops of sandstone and shale. The outcrops of sandstone are 

 usually characterized by a preponderance of bilberry (figure d}> 

 and those of the shale by swamps in which the larger rushes 

 (Juncus effusus and effusus forma compactus) are generally 

 conspicuous. The vegetation of these Juncus swamps has 

 already been described (see pages 146 150). Sometimes, even 

 in the general moorland area, a steep, shaly hill-slope is 

 characterized by siliceous pasture. 



The moorland vegetation ascends to the highest summits 

 of the district, three of which attain an altitude slightly 

 exceeding 2000 feet (610 m.). No Arctic or Alpine species 

 occur anywhere on the southern Pennines, as in the case of 

 the higher Pennine summit of Cross Fell further to the north 

 (Lewis, 1904 a: 328; 19046: 279). The vegetation of the 

 highest plateaux of the Peak District is marked by the 

 occurrence of retrogressive moors (figures 28 to 31) with much 

 bilberry (Vaccinium Myrtillus), which very often alternates 

 with patches of crowberry (Empetrum nigrum), less frequently 

 of cloudberry (Rubus Chamaemorus), and sometimes of bare 

 peat. 



The altitude to which the moorland vegetation descends is 

 determined partly by physiographical and partly by artificial 

 causes. Where the moorland ceases abruptly and is separated 

 merely by a stone wall from the permanent pasture of the 

 upland cultivation (see figure 24), the lower limit is simply 

 the place where reclamation has stopped ; and this limit usually 

 varies from about 1000 feet (305 m.) to about 1600 feet (488 m.); 

 but where the moorland adjoins siliceous pasture, the limit is 

 a perfectly natural one. The latter limit varies from about 

 750 feet (229 m.) to about 1500 feet (457 m.). Where the 

 moorland descends to the lower of these altitudes, a zone of 

 heather moor invariably occurs ; and where the moorland ceases 

 at the higher of these altitudes, this zone is absent. 



In ascending the lateral slope of an upland valley, the change 

 from the grassy slope to the peaty plateau is rather abrupt, 

 and the transition region narrow. This is well seen in an 



