122 VEGETATION OF THE PEAK DISTRICT [cH. 
Analogous vegetation occurs, of course, on the grasslands 
of the sandstones and shales. However, the details of British 
grassland associations, or groups of associations, have not yet 
been fully investigated. 
On the limestone plateaux, such tracts of grassland are 
frequently characterized by the great abundance of the mountain 
pansy (Viola lutea and V. lutea var. amoena), which, in early 
summer when the plant flowers with great exuberance, gives 
rise to a distinct facies or aspect. 
Transitional Calcareous Grassland 
At still higher altitudes (about 1100 feet = 335 m.), a type 
of pasture occurs which is transitional between calcareous 
grassland and siliceous grassland. A certain number of heath- 
loving or humus-loving species, such as Luzula multiflora, 
Potentilla erecta, Polygala serpyllacea, and even Ulex Galli, 
and also a certain number of lime-loving species, particularly 
Poterium Sanguisorba, may occur; and, under these circum- 
stances, such grassland may be regarded as transitional between 
calcareous and siliceous grassland. Such grassland occurs also 
on the Carboniferous Limestone in Yorkshire. Analysis shows 
that the superficial soil of such localities is comparatively poor 
in lime, even when the subsoil consists of limestone, and, as 
stated in the introductory chapter, even when there are no 
glacial or other foreign deposits. Doubtless the soil, in the 
course of ages, has had much of its lime carried away in 
solution. This type of grassland is, on the vegetation maps, 
given the same colour as that used. for siliceous grassland. 
CALCAREOUS HEATH 
Where the lime-content of the superficial layer of soil is 
still lower, such dwarf-shrubs or under-shrubs as the heather 
(Calluna vulgaris) and the bilberry (Vaccinium Myrtillus) may 
occur; and thus transitions occur between calcareous grassland 
and heath. This transitional association may be termed a 
calcareous heath. The association occurs on the Carboniferous 
Limestone in Somerset (Moss, 1907 a: 46), usually at altitudes 
above 600 feet (183 m.), below which altitude, typical calcareous 
