106 VEGETATION OF THE PEAK DISTRICT [CH. 
I. GRASSLAND OF THE SANDSTONES AND SHALES: 
SILICEOUS GRASSLAND 
Two types of siliceous grassland have been described in 
previous botanical surveys of the Pennines (Smith and Moss, 
1903: 384; Smith and Rankin, 1908: 158; Lewis 1904 a: 323, 
1904 6: 275), and have been distinguished as wet and dry. 
The most abundant and characteristic grass of the drier type 
of siliceous grassland is the mat-grass (Nardus stricta) and 
that of the wetter type is the purple moor-grass (Molinia 
caerulea) (cf. figure 14). The two species are respectively 
dominant in the two associations since they nearly monopolize 
the ground and form the great bulk of the turf, the asso- 
ciated species being therefore more or less controlled by them. 
The former association may therefore be termed Nardus grass- 
land (Nardetum strictae) and the latter Molinia grassland 
(Moliniétum caeruleae). To some extent, the associations are 
layered plant communities; and the smaller plants receive a 
certain amount of shade and shelter from the dominant ones. 
As is usual in plant associations, one or another of the 
dependent species occasionally becomes more or less social ; 
and thus plant societies and facies arise. 
(1) Nardus Grassland 
Typical Nardus grassland (see figure 13) occurs on steep 
shaly slopes of the non-calcareous hills. In summer, this 
association is characterized by a grassy turf, grey-green in 
colour, dry and slippery. In late autumn, winter, and early 
spring, the ground is damp and sodden; and the bleached 
haulms of the mat-grass (Nardus stricta) give tone to the 
landscape, and may be recognised at a considerable distance. 
The silver hair-grass (Deschampsia flexuosa) is, in this district, 
a constant associate. In winter, the mat-grass is very much 
more conspicuous than the hair-grass, as, during this season, 
the short leaves of the latter are usually more or less hidden 
beneath the long, white sprays of the dead shoots of the former. 
Under such conditions, the hair-grass, even though very 
abundant, is apt to be overlooked. It is only in early summer, 
when the tall, purple scapes of the hair-grass are in bud, flower, 
