140 VEGETATION OF THE PEAK DISTRICT [CH. 



the name qf Gerollflur or Gerollflora or Schuttflora (cf. Ottli, 

 1905: 18). Brockmann (1907 : 290 1) subdivides his " forma- 

 tions group " of the Gerollflora into plant communities (a) on 

 siliceous rocks, and (6) on calcareous rocks, and gives lists of 

 plants for each subdivision. It may well be that in districts 

 like the Alps, where the great differences in altitude produce 

 very marked differences in the vegetation at different heights, 

 the vegetation of the Alpine boulder-strewn ground belongs 

 to a different plant formation from other parts of the mountain 

 slope; but in this district, where the differences in altitude 

 on the limestone hill-slopes are comparatively slight, and 

 where the depth of the debris of stones is rather insignificant, 

 the plant communities seen on the screes can scarcely be 

 separated from those on the other parts of the hill sides (cf. 

 figure 21). 



SANDSTONE ROCKS AND SCREES 



Screes and boulder-strewn slopes also occur to some extent 

 on the siliceous slopes below escarpments of the Carboniferous 

 gritstones ; but here also the flora partakes of the same general 

 composition as that of the associations in close propinquity. 

 For example, the sandstone screes in the moorland area are 

 characterized by such plants as Calluna vulgaris, Vaccinium 

 Myrtillus, V. Vitis-idaea, Arctostaphylos Uva-ursi, and Des- 

 champsia flexuosa, which are rooted not on the bare sandstone 

 rocks but in the soil in which the boulders are embedded, 

 or in the clefts of the rocks, or on soil which has accumulated 

 on the projecting ledges. 



Most of the sandstone rocks and screes of the district occur 

 in the moorland area. Occasionally they occur in woods, and 

 only rarely in the grassland or cultivated areas. As in the 

 case of the limestone rocks and screes, the plants present 

 belong for the most part to the adjoining associations. For 

 example, on the numerous " edges " or sandstone escarpments 

 of the moorland area, humus collects in the rocky crevices, 

 and on the rocky ledges; and here moorland plants prevail 

 (see figure 19), particularly the bilberry (Vaccinium Myrtillus). 

 The same remark applies to the sandstone screes of the moor- 

 land area, though, as these receive a considerable amount of 



