VII] MOORLAND ASSOCIATIONS 175 



to the drier habitats of these species as compared with the 

 habitat of the cotton-grasses (Eriophorum spp.) and their 

 ecological allies. In the transitional moors of heather and 

 cotton-grass, the shallow roots of Calluna vulgaris, Vaccinium 

 Myrtillus, and Empetrum nigrum allow of their growth side 

 by side with Eriophorum vaginatum whose functional roots 

 are more deeply embedded in the peat ; for, in summer and 

 autumn, the upper layers of peat are frequently dry whilst the 

 lower layers remain extremely wet. 



(7) Changes in the habitat. It has already been stated 

 that the peat on the highest moors is in a state of denudation 

 and now dominated by Vaccinium Myrtillus, Empetrum nigrum, 

 and Rubus Chamaemorus. An examination of the plant-remains 

 composing the peat of such associations proves that the vegeta- 

 tion was previously dominated, and almost exclusively dominated, 

 by Eriophorum. The degeneration of an Eriophorum moor 

 results in the peat becoming drier; and this results in the 

 dying out of the more hydrophilous species, such as Erio- 

 phorum vaginatum and E. angustifolium and the successful 

 invasion of other plants, such as the bilberry, which are 

 structurally better adapted to the drier conditions. 



(8) Rainfall. It would appear that the local differences in 

 the mean annual rainfall of the different parts of the moorland 

 area have little or no relation to the local distribution of the 

 different moorland associations in the Peak District. Generally 

 speaking, the mean annual rainfall of the moorland area varies 

 from about 40 inches (102 cm.) per annum to 55 inches (140 cm.) 

 or rather more. It has been suggested (Smith and Rankin, 

 1903 : 155) that the areas where the heather (Calluna vulgaris) 

 is dominant have, on the whole, a lower mean annual rainfall than 

 the areas over which the cotton-grass (Eriophorum vaginatum) 

 is dominant ; but, judging from the statistics supplied by Dr 

 H. R. Mill (see page 25), the suggestion does not appear to be a 

 fruitful one so far as this district is concerned. It is well known 

 that the highest local rainfall of a district is not exactly at the 

 summit of a hill, but some distance to the leeward of that hill. 

 For example, in the present district, the highest indicated 

 rainfall (see British Rainfall) is not on the Peak itself, but 

 m Fairbrook Clough, which is a few miles to the leeward, that 

 is, to the north-east of the Peak ; and this tract of highest 



