176 VEGETATION OF THE PEAK DISTRICT [CH. 



local rainlall is characterized by a Avell-developed and typical 

 heather moor. Again, whilst the vegetation maps of districts 

 north of the Peak might, if taken by themselves, be held to 

 indicate that the heather moors were characteristic of the 

 eastern and not of the western Pennines, it will be seen that 

 that indication is not borne out by the vegetation maps of the 

 present district. The comparative dryness of the peat of the 

 heather moors is to be explained, not by rainfall statistics, but 

 by the larger proportion of silica mixed with the peat of the 

 heather moors, and by the greater shallowness of the peat. 



Heather Moors 



Associations dominated by the common heather (Calluna 

 vulgaris) are among the most typical plant associations of the 

 British Isles. In a general way, such associations may be sub- 

 divided into heaths and heather moors, the former occurring on 

 soils containing a higher proportion of sand and which are 

 therefore drier, and the latter on soils containing a higher 

 proportion of acidic humus and which are therefore wetter. 

 In general, heaths are characteristic of the south and east of 

 Britain, heather moors of the north and west. Hence, the 

 occurrence of heath and of heather moor in this country would 

 seem to be determined to some extent by climate. The 

 associations of Calluna vulgans (see figure 22), which so often 

 occur as a fringe of the Pennine peat moors, are, on the whole, 

 heather moors and not heaths, though some of those found at 

 lower altitudes approximate in character to heaths. 



Weber (1908 : 91) suggests that the term moor should be 

 used only when the peat is 20 cm. or more in thickness and 

 when there is less than forty per cent, of ash [including silica] 

 in the peat ; but a too rigid use of these criteria lead to an 

 artificial classification. 



Beginning at Hayfield, what may be called the western 

 system of heather moors extends northwards for about ten miles 

 (16'1 km.), their continuity being broken by the narrow but deep 

 clough formed by Shelf Brook, and by the larger Longden- 

 dale, formed by the river Etherow. The northern slopes of 



