140 VEGETATION OF THE PEAK DISTRICT [CH. 
the name of Gerdllflur or Gerdllflora or Schuttflora (cf. Ottli, 
1905: 18). Brockmann (1907 : 290—1) subdivides his “‘ forma- 
tions group” of the Gerdllflora 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 débris 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-cdaea, Arctostaphylos Uva-ursi, and Des- 
champsia flecuosa, 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 
